Materials for the Study of Variation Treated with Especial Regard to Discontinuity in the Origin of Species

A specimen, also Belgian, is described in which the two anterior wings resemble Herrich-Schaffer's figure in lacking the white bars on the costre and in the arrangement of the black and ground colour. In neither of them are the white spots of the anal angles (found in the British and Australian specimens) present. The white markings at the apex of the anterior wings differ on the two sides, being in both of them unlike the type and an approach to the aberrations in question, but the degree to which they are developed differs markedly, being greatest on the right side. The left posterior wing resembles the aberration in having the six abnormal white spots, but less emphasized than in the figures quoted above ; in general colour this wing is darker than the type. The right posterior wing, however, has none of the white spots of the aberration, and differs from the type only in being more suffused with

1 : tulut. -.tintwo anterior and tlie left posteriorwing resemble generally, ration, while the right posterior wing is nearly normal . -itiiik' tl.. Minsverse band and in the disposition of the apical •in- \vhit<- costal bar remains on the costal border. On the : .ire aberration " var. Elymi" there is a variety sometimes found in I i.j,' may be quoted respecting its occurrence iu Australia, • I .... .1 mdance about Melbourne aud in many other parts of Australia

il appearance and habit of C. cardui, so closely represented I know refers it to that species. The Australian species diiT.ii fii.ni tl,.- Kiii.ip.an one constantly, however, in having the centres of the thi. : >ts on the posterior wings bright blue, and having two other bin. ior angles of the same wings, the corresponding parts of in Kiir»|. r iiiluw-i. In 1884 Mr Jenner Weir exhibited a specimen of P. Nr\v Forest. Three of the five black spots in the disk of the

ii)i]" :' thr biii'l-wings had blue pupils ; lie pointed out that the specimen tliat he has taken a specimen having these blue at K.i: \\ijk, in Holland. In tincase i,ri\eii, the evidence certainly suggests that these \.-iri'. M^ forms M aberration are grouped round a normal form of ab.-iTatiiin, jii>t a- tinindividuals of the type are grouped round may pn.titably li«- given. I have taken this opportunity of referring to such a case, as the general evidence of melanie \ariati. .n- :i the whole to she\\- that they are not commonly

discontinuous, and further e\idenee <>n this point would be most. '!'•• appreciate the evidence BUTLER'S coloured plate A \M-11 inarkr.l LTi-,,up (»f butterflies of this genus allied to , i^ f.iiiii.l in .Japan. It cmitaiiis funns of great diversity in amount of Mark l.onlrr whi.-li on-ni-s mi tinouter margins of the fore- I'onl.T may !,.• confined bo the tip .,f tinfore-wings, or may there OOCUpy a .-on, i.l. -ral.lc ana ami 1 »• extended alon^ the whole outer

mar-in of l-.,tl. wri Tli.- for,,, with thr least Mark is called T. mantl.at with tinmost, is i-ullr.l /'. OTortewt, and the intermediate • examined; th,-M- ran-nl between the bwo extremes, and were fllllnii '" ' ...... :i continuoua series. Botler states that " the absence of them, referable ..nly to two gradations, w,,ul«l at once leave the three specie sharply <leiim-<l as anv in the ^-nus." '" ''"' ' these butterflies, there are thua ' ll1" groups of varieties

- extreme jroupa .-,,„! ,„„- mean group j intermediates between these tare comparatively rare. Butler suggests that these intermediate forms should be regarded as hybrids, even in the absence of experimental evidence. This view is of course dependent on the truth of the belief that such a discontinuous occurrence of variations is anomalous.] Twenty specimens of the species T. betheseba and thirty-nine of T. jaeyeri (botli from Japan), were also examined. The former presented no variations whatever, and the latter only vary in the yellower or redder tint on the under surface of the secondaries. BUTLER, A. G., Trans. Ent. Soc., 1880, p. 197, PL vi.

Terias constantia. Twenty-five pupse, all found together on the same twigs at Teapa, Tabasco, Mexico, by Mr H. H. Smith. The butterflies from these are in Messrs Godman and Salvin's collection, who kindly allowed me to examine them. The amount of black border on both wings varies much, nearly though not quite so much as in the cases figured by BUTLER. In the lightest the apex of the fore-wing alone is black, and there is no black on the hind-wing in 9 specimens ; of the remaining 16 some have a well-defined black border to the hind-wing, while in the rest (about 6) this border is slight. This case is a particularly interesting one, as the specimens were associated and presumably belonged to one brood.

For another beautiful case of discontinuous Variation in pattern I am indebted to Dr D. Sharp. The Cambridge University Museum lately received a series of 38 specimens of Kallima inachys, the well-known butterfly whose folded wings resemble a dead leaf with its mid-rib and veinings. The underside of this butterfly is sometimes marked with large blotches and flecks of irregular shape, which, as has often been noted, resemble the patches of discoloration caused by fungi in decaying leaves. Dr Sharp pointed out to me that the specimens examined fell naturally into four groups according to the coloration of the underside. In the first group the field is nearly plain, though the tint varies in individuals. The " mid-rib " is strongly marked in this and all the groups, but the " veinings " are absent or very slightly marked in the first group : 18 specimens. In the second group the ground is almost plain, but it bears numerous strongly marked black-speckled spots, of forms which though irregular in outline are closely alike, and occupy the same positions in all the six specimens, being scarcely if at all represented in any of the others. In the third group the dark bars representing " veins " are strong, but the field is nearly uniform : 10 specimens. In the fourth group, of four specimens, the ground-colour is darkened in such a way as to leave large and definite blotches of light colour in particular places. Of these specimens three have the veinings very strongly marked, while the fourth is without them.

Into these four groups the specimens could be unhesitatingly separated, though in each group many individual differences ,11. .1. No mark. (1 \ariati.ui in th-- upper-ides was to be seen. perimenwere all from th«- Khasia hill-. Assam, but thenno evidence that all were tl\ing to-vthcr. manif.-tations aninanv and diverse. We have seen that in such features as si/.', ••<,!,. nr, and culoni--|iat tej-ns, Variations may be • li-.-. nit inn.. ii-. and a form may thus result, differing markedly iVi.m tin- t\|>.- which begot it. Variation in the proportions or tin- ••..n-titutiiui «.f .-s.-ntial jiart> may no less suddenly occur. 'I'll, ran^.- ..!' tln-se jiheiniini-iia is a large one, but. tor the purposes <>f thi- Iiitmdnetion :i few • xampl.-s must suffice in general illustration of their scop.-.

A discontinuous variation which is familiar to all is that of rersed" vaiieties, ojiecially of MolhiM-s and Flat-fishes. Such \ ari'-t 1- - anformed as ..jit ieal ima^i •> of the body of tin ' type. In both ..f tin- ^n.nps nann -d, >ome species are normally right-handed. ntln-r- l.ein^ normally left-handed, while as individual variation-- rev. i-. d . samples are found. In .Molluscs this is not peculiar to 1 .pods uith spiral shells, but may occur also both in Lima-

cid.-e islii;^-)1 and in Laim •llibraiichsa. Such variation is commonly discontinuous, and th«- two conditions are alternative. The fact that the reversed condition may become a character of an establi-hfd pace isfamiliar in th.- case of /'//*//* untufinis. This shell is toiind in abnndanc.- as a fossil of the Norwich Crag, such iin.il-> K. innormally 1.1't-handed. though the same species at th.- pr..-eiit da\ i- a ri-hthanded one. Of the left-handed form a CO|MI,\ was discovered \>\ MAI-ANI>I;I:\V on the rocks in Vigo Bay::.

was there a.—oeiated with certain other shells proper to the N"i \\ich ( Iraff. This discovery BI .-mL-d to Edward Forbes to be so remarkable that he looked ,,n it as corroborative evidence of a |;d connexion between the fauna of Vig.> Bay and the Crag fosailfi . Jeffreys had the same variety from Sicily4. That they may the better serve to bring out the significance of Discontinuity in Variation to the general theory of Descent, it may be well to choose some examples with reference to characters which when seen in domestic animals are looked on as especially the result of Selection.

In exoskeletal structures several of this kind are known. From time to time there have been records of captures of the " hairy variety " of the Moorhen (Gallinula chloropus), in which the feathers were destitute of barbules and consequently had a hairy texture, greatly changing the general appearance of the bird. Of the " hairy " variety twelve specimens were recorded, five from Norfolk, and the rest from Cambridgeshire, Hampshire, Sussex (2), Suffolk, Nottinghamshire and Athlone in Ireland. The tips of the barbs and shafts of the feathers have been broken off and the barbules are entirely wanting, giving a hairy appearance. This appearance was found in the whole of the plumage. Owing to the absence of barbules, the general coloration is tawny. A few feathers of this kind have been found in Hawks and Gulls, and in the case of a Parra (a bird which bears considerable resemblance to a Moorhen), lent to Mr Gurney by Professor Newton, a great portion of the body feathers were in this condition. The feathers of the Apteryx and Cassowary are also partially destitute of barbules. Mr Gurney was informed of a single case of a Grey Brahma hen which shewed the same peculiarity which appears otherwise to be without parallel. The case of the Silky Fowl is similar in the absence of most of the barbules, but in it the point of the shaft is produced to a delicate point, and the barbs are fine and sometimes bin'd or tritid at the apex. From J. H. GURNEY, Trans. Norwich Nat. Soc., in. p. 581, Plate. [Bibliography given.] [If another " hairy " Moorhen is found, note of the colour of the skin and bones should be made, for, as is well known, in the Silky Fowl they are purplish blue.]

The following may be compared : " Cochins are now and then met with in which the webs of the feathers having no adhesion, the whole plumage assumes a silky or flossy character like that of the Silky Fowl. It usually occurs quite accidentally, and in every case we have met with, the variety has been Buff. By careful breeding the character can be transmitted, but we have only known one case in which there had been this hereditary character, the others having been of accidental occurrence. Such birds are sometimes called 'Emu' fowls." LEWIS WRIGHT, Illust. Book of Poultry . 1886, p. 230.

Of many domestic animals, for example, the goat, cat and rabbit, varieties with long, silky hair are familiar under the name of " Angoras." Very similar breeds of guinea-pigs are kept, to which the name " Peruvian " is given. In this connexion the capture of a mouse (Mus musculus) with long, black, silk-like hair is interesting1, as shewing that such a total variation may occur as a definite phenomenon without Selection. 1 COCKS, W. P., 2 Van*. Cornwall Pulytech. Soc., 1852. Like other animals, mice have of course often been found black. For instance, a number of black mice were found in Hampstead-down Wood. HEWETT, W., Zool. Jour. iv. p. 348.

AJ to the partial nakedness of the skin of many animals iMiin A.-.», several suggestions have been made. It has been variously supposed that the covering of hair has been gradually lo.t l.\ 'Man, in correlation with the use of clothes: with the heat the MIL. f..r ..rnaiii.-ntal purposes under sexual selection1; or !„ rl.ap- a* a protection from parasites'. Various suggestions h:i\.- also been made to explain the persistence of hair at the jun.-ti..n of the limbs and mi the head and face. To a con- Vidi-rati..!! »f the origin of nakedness, the evidence of Variation in ,.-asure contributes, and though the bearing is not very dir. n. it may illustrate the futility of inquiries of this kind made without n-gard to the facts of Variation.

IfoUBB (J/"." miisculu*): male and pregnant female found in a ..-k lit Taplow ; both were entirely naked, being without hairs tlir..\\n up into numerous prominent folds, transversely traversing the Imdy iii :tn undulating manner. This condition of the skin obtained f,, r "tilt-in tinname of "Rhinoceros mice." The ears were dark or hla.-kish, ill-1 'ail ash-coloured, and the eyes black, indicating that they we,,- i,.,t .-illiino-. The exfoliations from the skin were examined

iiiicrosco pit-ally but no trace of hair-follicles was found, nor any Tinvoting ones, when born, were similar to the parents. The Tin---'- -p.-.-i ..... n-. of tin- i-ciiiiintin Mouse (Ma* ///».•«•/////*) were caught in tintown i if Kliiin. The whole bodies of these three creatures "were .-..nipleti-lv naked as destitute of hair and as fair and smooth as a rhild's t-hft-k. Thenwas nothing peculiar about the snout, whiskers, , l.iwcr half of tin- It-u's and tail, all of which had hair of the usual length an. I ctilmir. They had eves a.- bright and dark as in the common variety ..... At least twn others were killed in the same house where th- f<>und." CoiMiov. <... Z",,/,»//.s7, 1S.~>(), viii. p. 2763.

>m.i\v (SoreX •'p.) "whole of upper surface of head and body I ' ..... M teri/fil liy |n.--essiiie an a|i]Mi . nily hairless skin which is on the I ami limly nf a wrinklnl iiml \varly nature. On elusrr in>]iection the skin is . t.. lie fiiiiii-he.l with Inn -< ;i!iei. il liairs. luit there is no general appearance of a Imirv t-overing. Th. re i> no external ear in these animals. OLDFIKLD THOMAS, Iced honea lia\e often been exhibited. Such a horse caught in a

semi-feral herd in Queensland was described by TEGETMEIER, Field, XLVIII. 1876, p. 281. The skin was black and like india-rubber. Careful examination shewed no trace of hair, or any opening of a hair-follicle. In Turkestan, in the year 1886, I heard of one thus travelling, but failed to see it. 'Hairless' dogs in S. America remain distinct (BELT, I. c.). Of discontinuous Substantive Variation in bodily proportions a single example must suffice. Among domestic animals of many kinds, races are known in which the bones of the face do not grow to their full size, while the bones of the jaw are, or may be, of normal proportions. Familiar examples of this are the bull-dog, the pug, the Japanese pug, the Niata cattle of La Plata1, some short-faced breeds of pigs, and others. In the case of these domestic animals the part which Selection has taken in their production is unknown, and the magnitude of the original variations cannot be ascertained. It is nevertheless of interest to notice that parallel variations have occurred in distinct forms, and I think that this is to some extent evidence that the variations were from the first definite and striking. As regards the dogs even, there is a presumption that the short face of at least the Japanese pug arose independently from that of the common, or Dutch pug (as it used to be called), but as to this the evidence is insufficient. Among the dogs' skulls found in ancient Inca interments, a skull was found having the form of the bull-dog. NEHRING, Kosmos, 1881, xv. As these remains belong to a period before the European invasion, it is most probable that this bull-dog breed arose independently of ours.

Apart however from domestic animals there is evidence as to the origin of short-faced breeds. This evidence, which is not so well-known as it deserves to be, is provided by the occurrence of a similar variation in fishes. Darwin in speaking of the evidence as to Niata cattle makes allusion to the case of fishes in a note2, quoting WYMAN as to the cod, which occurs in a form known to fishermen as the "bull-dog" cod. The interest of this observation is increased by the fact that it does not stand alone, but similar variations have been seen in the carp, chub, minnow, pike, mullet, salmon and trout. In the last-named there is even evidence of the establishment of a local race having this singular character.

CARP (Cyprinus carpio). " Bull-dog "-headed Carp have often been described. The face ends more or less abruptly in front of the eyes, while the lower jaw has almost its normal length. The front part of the head is bulging and prominent, giving the fish an appearance which several authors compare to that of a monumental dolphin. A good figure of such a specimen is given by G. ST HILAIRE, Hist, des Anom., ed. 1837, I. p. 96, where a full account of the older literature of the

subject may be found. Inasmuch as carp are largely bred in ponds on tin'ent, there is in this case some suggestion that unnatural •M.-iy be concerned, but this suggestion does not apply to other th.it in the ponds of Silesia such tish are not rare. See also VOK;T, Th. id was protuljerant and bulged in front of the eyes so that mandible are carried forward in such a manner that the mandible Sevi ,1 other types of Variation in the heads of Cyprinoids occur, but i-.iniii't In- d'-M-ribed liere.]

i in i; i /.• " ••i-rim dnbula = cephalus) : specimen having anterior part MINNOW (1'hu.riuns hn'ix) specimen having a snout like a pug in"jme") [no description]. LUNEL, Pom. dulacLeman, p. Mi 1. 1. 1 i i Mmi'd capito) : specimen having both jaws directed up \\.ml-, ami the upper and anterior parts of the skull greatly i •!• -v.iti-il ainl protuberant : the appearance of the head was like that /'/" ' urioufl nialt'ocniat ion of N. frulto il)id ], see also Jahrb. Ver.

occur in neighbouring lochs. None weighed more than \ Ib. YAKKELL, Brit. Fishes, i. p. 286, figure given. Another specimen (Fig. 6), agreeing closely with Yarrcll's figure, was taken in a lake at an altitude of over 6000 ft. in the valley of Sept-Laux (Isere). Saving the head it was in all respects normal. This specimen is described and figured by CARLET, M. G., Journ. de I'Anat. et Phys., 1879, xv. p. 154. [It is declared that the fishermen who took it, having previously met with similar specimens, supposed that they had found a new species, but it is not expressly stated that these other specimens were from the same locality.]

Before ending this preliminary glance at Discontinuity in Substantive Variation, allusion must be made to a case which is at once more famous and more instructive than any other. I refer to the celebrated phenomenon of the production of nectarines by peaches, or conversely. Upon the subject of almond, peach and nectarine, Darwin produced a body of facts which, whether as an example of a method or for the value of the facts themselves, form perhaps the most perfect and the most striking of all that he gave.

The evidence which is there collected is known to all, and though similar observations have been made since by many, there is I believe nothing of importance to add to Darwin's statement. The bearing of these phenomena on the nature of Discontinuity in Variation is so close that Darwin's summary may with profit be given at length. " To sum up the foregoing facts ; we have excellent evidence of peach-stones producing nectarine-trees, and of nectarine-stones producing peach-trees — of the same tree bearing peaches and nectarines — of peach-trees suddenly producing by bud-variation nectarines (such nectarines reproducing nectarines by seed), as well as fruit in part nectarine and in part peach, — and, lastly, of one nectarine-tree first bearing half-and-half fruit and subsequently true peaches"1. After disposing of alternative hypotheses he concludes that " we may confidently accept the common view that the nectarine is a variety of the peach, which may be produced either by bud-variation or from seed."

In this case the evidence is complete. The variation from peach to nectarine or from nectarine to peach may be total. If less than total, the fruit may be divided into either halves or quarters2, so that for each segment the Variation is total still. Of intermediate forms other than these divided ones, we have in this case 2 Ibid., p. 362, quoting from London's Gurd. Mag. 1828, p. 53. The case of a Boyal George peach which produced a fruit, " three parts of it being peach arid one part nectarine, quite distinct in appearance as well as in flavour. " The lines of division were longitudinal.

no evidence: it is therefore a fair presumption that they are eith.-r rannr non-existent ; and that the peach-state and the •arin. -state are thus positions of " Organic Stability," between \vhi.-h th.- intermediate states, if they are chemical and physical These examples of Discontinuity in Substantive Variation iiui-t Mittire to illustrate the nature of the phenomena. It will be M that the matters touched on cover a wide range, and the evidence relating to them must be considered separately and at l.-n-th. Such a consideration I hope in a future volume to attempt.