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

[P. vitulina: nlv.-nlus tur left /'' much larger than that for rt. Pl; the latter tootli is in place, but Irft /•' is missing. C. M., IIU'2.] P. groenlandica : in the position in which left upper ;?4 should stand there are two whole and complete teeth, each as large as normal l>\ Fig. "•"). The two stand perfectly in series, and owing to the wide gaps normally existing between the teeth in this species there is no crowding. Between these two teeth there are slight differences of

FIG. 57. Phoca fjrcenlandtca, No. 324. Left and right profiles. This figure was kindly drawn for me by Mr J. J. Lister. form, and the posterior is rather the larger. On both sides "^ is in place and at the same level. Both the two teeth in place of F4 bite between fi and ^ of the lower jaw. On the right side F1 is normal and "^ is also normal but F* is a very large and thick tooth, and its main cusp is cloven, giving it the appearance of imperfect division into two. In this case therefore F1 on the one side may be supposed to have divided into two perfect and nearly similar teeth, while on the right side this division is begun but not completed. Leyd. M.

325. Otaria ursina £ : supernumerary premolar in left upper jaw. This is a curious case. The right upper and both lower jaws are normal. On comparing the left upper series of 7 teeth with the right series which has 6 normal teeth, it is seen firstly that the two molars of each side are alike in form and stand at their proper levels (Fig. 58). FIG. 58. Otaria nrsina, No. 325, seen from left side. lower prernolars ; 5, lower molar. the two posterior premolars of each side (F^ and F4) agree so that there is no reasonable doubt that they are not concerned variation. Anterior to this there is difficulty, for whereas pl are normal and in place on the right side, there are tJiree teeth left side to balance them. These three teeth moreover are so alike that it is impossible to say that either of them is

definitely tinextra tooth. The first pi. -molars of each side are almost exactly alike, and tin- .-eeond an. I third of the left side are each very likitinsecond ..n tinright side (jr), so that it might be said that //-' was represented l>y two teeth on the left side; and as seen in Fig. •">* tinsecond and third on tinleft side bite between p and p* of the lower jaw. as tinnormal IT would do. This is however accomplished by the liack \\ard displacement of ^5. Probably therefore this should be looked on as a case of division of 1^, but there is no proof that the three first premolar.s «,f tinleft side are not collectively equivalent to the tir-t two ..f tli.- ri-Jit side. C. M., 911, f.

P. groenlandica : the second upper right premolar is represented by two teeth, each of which has two roots; the two teeth stand at the same le\el in the arcade, the inner one being rather smaller. On the li-t't -id.- the second uppeipremolar is incompletely double, the crown I.ein^ partially divided by an oblique constriction into an anterior and internal pun imi and a larger posterior and external part. The former has uiie mut and the latter two. P. M.., A, 2897.

Otaria jubata : left upper y/:i a bigeminous tooth something like the anterior preiimlars of Ommatophoca (No. 320). In this animal all the preniulai-s and molars are one-rooted and have simple conical crowns. The abnormal tooth is formed as it were of two such simple teeth imperfectly <li\ide<l from each other through their whole length, the plane of division being transverse to the jaw. The teeth of the two .sides are not alike and in particular the posterior lower wT1 is much smaller than the right. The skull has been much mended and the posit iun .if sum.- of the teeth is not very certain, but the abovementioned t'aets are correct. C. 8. M., 97-X

Otaria cinerea : supernumerary tooth in upper jaw on both sides. The extra tooth in each case stands within the arcade, internal to the itturin cinerea, N<>. H28. A diagram of the positions of the upper <>f the tn-th standing inti'iiial to each we\ •~'th tooth behind the canine (sc. "/'). which is pushed outwards by it. The extra tooth of the left side ( Ki-. .V.I) is a little larger and at a level rather anterior to that of the left extra tooth. C. M., 911**.

*329. P. vitulina : having a supernumerary tooth in each jaw on the right side. This is a somewhat remarkable case. In both jaws the extra tooth does not stand in series with the others but is placed within the arcade (Fig. 59, + + ). That of the upper jaw is a curved tooth with one large median cusp and a small cusp anterior to and posterior to it, having somewhat the form of p* of the lower jaw. This tooth stands within the arcade at a level between that of 1^ and p! which are pushed outward by it. The extra tooth of the lower jaw in shape closely resembles that of the upper jaw, but is slightly larger, having very much the size and shape of the lower right p*. In position this extra tooth does not stand between p2 and p3 like the upper supernumerary, but is placed within the arcade and p^ and ]74 which are somewhat separated by it. C. M., 903. [Judged by the ordinary rules of dental homology, the two extra teeth are not homologous, for the upper one is between p- and ps, while the lower one is between p and /A But when the jaws are put together it appears that the two extra teeth are opposite to each other almost exactly, the large cusp of the lower one being in the bite scarcely at all posterior to the large cusp of the upper. The tooth of the lower jaw is thus almost exactly the image or reflexion of the tooth in the upper jaw.]

FIG. 60. Phoca vitulina, No. 329 ; view of upper teeth from the surface, and an imaginary profile of the upper and lower teeth of the right side seen from within. 330. Otaria ursina : this skull in bad condition. The Catalogue (1884) states that between r and F* on both sides and between F4 and m± on both sides there was a small supernumerary tooth, in all, four extra teeth in the upper jaw. The anterior supernumeraries are in place and one rather smaller than p^. The posterior supernumeraries are lost, but from the alveoli they must have been of fair size, though not so large

a- y1. Iii each c;isf tinextra tooth is placed a little within the arcade though the adjacent tn-tli analso spaced out for it. This skull has 331. Phoca groenlandica: in ri^'lit upper jaw 7^ is smaller than the corresponding 1 of tin left side, though it is two-rooted as usual. Between it and p? there is a siii;ill. jn-^-likf, Mi]H rniiiin i.u-y tooth. Both pj and the extra tooth bite between ,,• mid ,„' of the lower jaw. Li-ijd. M. 332. P. grocnlandica : .-U]M nuimerary tooth with two roots placed internally to and between left /'' and »<\ The last molars stand at the same level on the two sides. B. M..32S, i.

333. Zalophus lobatus: in ri<iht upper jaw a supernumerary tooth placed on the i»iti<i'l<' of tin- ;tn-;ule nn a level with the interspace between p* and p*. This touth • or in1. On the left side p1 is smaller than on right side and a supernuineiaiy tniith wliieli is still smaller stands between p^ and the canine. L/'ijd. M. [given above, No. 323]. P. vitulina: in right lower jaw a supernumerary tooth inside the arcade, between J: :nnl /,-•. In size and form it agrees very nearly with the first premolar of the ri(_'ht lower jaw: other teeth normal. C. M., 903, F.

335. P- vitulina: in front of ^ on left side the teeth are all lost but there has been some irregularity, probably a supernumerary tooth level with j^: also behind ri;_'ht w»l there is a small tubercular nodule of bone which may perhaps cover a supernumerary molar. C'. .S'. J/., 1064. 336. P. vitulina : on left side there is a small supernumerary molar placed behind '»'. This tooth stands in the line of the arcade (Fig. 01) Kni. c,l. rhora rititlina No. 33G, a profile of the left teeth in the bite as seen from within.

but is turned si. that its greatest width is set transversely to the jaw. Tn the lower jaw of the same side there is a supernumerary tooth placed internally to „,'. This tooth has two roots and three cusps, and is therefore not a copy of ,n\ which has 4 — 5 cusps. C. S. M., 1007. < )f:{4 skulls in ( Jivit'swald .Museum there were 3 cases of m Of 11 skulls .seen l.y myself two individuals (C. M.) ha\c an extra molar on left side. In these eases the extra teeth are placed at^a considerable distance behind ^ as they are in Oturin. [In addition to tlies,' CKAY figures a skull with wf but without allusion (,, this fact in the text. ll<tml-Uxt of Seals in B M L874, I'l. vii.]

A skull having left ^ two-rooted, right »^ being much less so. 339. Zalophus californianus, an Eared Seal not far removed from Otarid, but having j? + mi instead of 4. The five back teeth are arranged as a rule in a continuous series, but sometimes there is a small space between the last molar and the penultimate [cp. 0. stelleri], and occasionally they are all slightly and evenly spaced. One case of p + »?4 on both sides and two cases of p + m~ on one side only. In these the extra teeth were behind the (normally) last molar and smaller than it, being without the accessory cusps seen in that tooth. ALLEN, J. A., N. Amer. Pinnipeds, 1880, pp. 209, 224 and

340. Z. lobatus : one specimen having p + ?n| on right and 4 on left, Leyd. M. [in addition to 3 specimens with the normal 4]. 341. Callorhinus ursinus : normally p + rafj one case having -— - 342. Arctocephalus australis, normally p + raf : one case of — = . General statement made that in cases of absence of a tooth it is the antepenultimate molar which is missing [not described in a specific case]. ALLEN, I. c., p. 224. 344. Otaria jubata, normally 4: one specimen having 4 on both sides, Leyd. M. ; one specimen having right f left 4. Leyd. M.

Cystophora cristata: only one molar, viz. left »il present; from the state of the bones it seemed possible that the others had not been formed, but this is quite uncertain. C. S. M., 1101. Macrorhinus leoninus: doubtful if the molars had been present. C. S. M. 1109. As to the occurrence of Variation in the dentition of Ungulates I have no statistics, but a certain number of miscellaneous cases have been collected from different sources. Most of the cases relate to domestic animals and are given on the authority of MOROT and GOUBAUX.

Perhaps the most interesting evidence is that regarding the change of form in the "canines" of the Sheep. These teeth of course have normally the shape of incisors, but in the cases described by Morot they had more or less of the character of canines. This evidence, though belonging properly to the Substantive class, is introduced here on account of its close relation to some general aspects of variation in teeth. It i-< noticeable that there is so far no case of an incisor appearin-- in tinii)i|n'i -jaw of Ruminants.

:it-">. Elephas africanus £ : the left tusk imperfectly doubled. The n..,t <it' tinninth was douUe1, one root being outer and the other inner. Tinhalf i if the tusk arising from the outer root twisted round and over tin- «>i)i»-r half so that at the other end it lay above and internal to it. 'I'll.- -tincture of the tusk was essentially double, but the two parts \\i-re more or less hlcmled together in the middle third. The external ends vsere separate, ljut broken and somewhat deformed. KI;IKI>I.O\\SKY, A., Sitzungsb. </. A'. Ak. Wien, 1868, LIX. i. p. 33.'?. Plate.

Horse. Supernumerary incisors common. MAGITOT, Anorn. tiyst. School at Alfurt. .'547. Specinifii having 12 upper incisors and 12 lower incisors belonging 71. Similar observation, LAFOSSE, Cours Hippiatrique, 1772, p. 32. .S4s. Extra teeth of more or less irregular form placed behind upper incisors very common : many specimens in museum at Alfort. Specimen ha\ing left '" as a double structure, the two halves not being of incisor in Horse is rare. GOCBAUX, who has largely studied the subject, knew no case of absence of any tooth in Horse, 1. c.

349. Skeleton of ( art-mare in C. M. has only two incisors on the left side in the ii]i|>iT ja\v. The teeth stand evenly and without break or trace of any other incisor having been present. There is no sufficient indication to shew which of the incisors is missing, lnit tlic two incisors present agree most nearly with i'2 and j3. This -p. run, n \\iifirst pointed out to me by Mr S. F. Harmer. (See also case given by Kri'oi.rin, An<it.-]ilii/.t. Al/li., 1802, p. 14.").)

*350. Marc of common breed, foaled March, 1876, having in the upper jaw no r in either milk or permanent dentition, and in the lower jaw no permanent i'3. In the upper jaw there were only 4 milk incisors, which were subsequently replaced by I pcimanent incisors. Animal seen by MOROT in Apr. 1880; it then had 4 permanent incisorin the upper jaw, but no i3. In the lower jaw permanent i1 and i- were in place, together with i3 of the milk scries on each side. As Morot remarks it is still possible that the other incisors might appear. Dam normal; half-sister ahiininial, given in n, \t case. Mouor. Hull. Sue. mnl. vft., 1885, Ser. 7, n. p. 125.

*.S5 1 . Mm" ""I of same mother as last case, by another sire, foaled Apr. 1877, had only 4 milk-incisorin upper jaw. Seen by Morot at 3 years old, had then the teeth o'f lower jaw animal, \i/. permanent ;', and milk /- and i3 all in place. In upper jaw \\ere permanent /' and milk /'-' on each side. The right milk /-'on the external side bad a light groove jiarallel to the long axis of the tooth, suggesting that it might be a double -tincture, but the groove \\its very slight and the crown was single. At five years old this animal had the. normal (i lower incisors, but in the upper jaw left /:i was absent. < *n the other hand a well-formed supernumerary tooth stood behind right r1, right /-' being partly rotated. Ibid., p. 127.

B also n curioiicase of " nine tusks " imperfectly described by CHAPMAN, J., ill Interior <>/ S. Ai'rifii, n. p. '.is. 352. Ass : ( $ some 20 yrs. old) on right side in upper jaw were two canines, one in front of the other in the same alveolus. MOROT, Kec. med. vet., 1889, Ser. 6, vn. p. 480. Another somewhat similar case, ibid. Goat, 4 — 5 weeks old ; supernumerary lower incisor placed between the two median incisors which rose above it. This tooth stood transversely so that its edge lay exactly in the long axis of the head. MOROT, I. c.

*355. In the lower jaw of the Sheep there are on each side 4 incisiform teeth, arranged in close series without any diastema. Of these the outermost, known in veterinary works as " corner teeth," are considered by zoologists as representing canines. The corner teeth or canines have been found in a considerable number of cases actually shaped like canines instead of like the incisors as usual. These teeth have been found presenting this modification in several degrees, but in order to gain a fair view of the matter it is necessary to read the evidence in its entirety.

The facts given were founded on 18 animals, 15 ewes and 3 males [whether rams or wethers not stated]. In these 18 cases there were 28 individual teeth of abnormal form. Of these 14 were conical with a point either sharp or rounded ; 7 were conical with a bifid point ; 5 were cuneiform ; 1 was cylindrical with a surface shaped like an ass' hoof; 1 was pyramidal. In 8 specimens the abnormality was unilateral and in 10 it was bilateral, but in the latter the corner teeth of the two sides were frequently of differing forms [details given]. MOROT, Bull. Soc. med. vet., 1887, p. 166.

Pig. No case of Variation in incisors met with. [This is perhaps singular in connexion with the fact that the Peccaries (Dicotyles) have i f .] *356. Dicotyles torquatUS (normally i'i) : two specimens having i o Q 5 m one °^ them i" of the side having the extra tooth is deformed. Another young skull of Dicotyles also had 3 incisors on left side. HENSEL, Sdugethiere Siid-Brasiliens, p. 94. 357. Horse: supernumerary molars exceedingly rare; case of such a tooth in left upper jaw, behind and in series with the others. GOCBAUX, AVc. med. vet., 1854, Ser. 4, i. p. 71, same case, figured by MAGITOT, I.e., PI. v. tix. 9.

*358. Ass: thoroughbred Spanish she-ass, in the Museum of the Royal College of Surgeons, has a large supernumerary molar on each side in series in the upper jaw, and a similar tooth in the left lower jaw. The ime skull has the first premolar also present on each side in the upper jaw, as is not unfreipjently the case in Equida?. All four canines are pre -. -nt as minute teeth. The dental formula for this skull is therefore 35!l. Auchenia lama: specimen having a supernumerary (fourth) molar in the lower jaw [?on both sides]. This tooth was fully formed and re.s.-ml.led the normal last molar. In the upper jaw was a small alveolus behind ?/i3, for another tooth which was not present in the specimen. ItfiiMKVKR, L., Vers. eitier naturl. Gesc/tichte des Rindes,

3(50. Cervus axis $ : specimen having a supernumerary grinder placed on the inside of the normal series on the left side of the upper jaw. In the lower jaw of the same specimen the following supernumerary teeth: (1) a small, compressed accessory tooth on both sides placed internally to w- ; and (2) behind the large three-fold sixth molar was a -mailer two-fold tooth which had caused a displacement of the 6th molar. hoxrrz, Sitzungab. d. iiaturf. Fr., Berlin, 1872, p. 54.

361. Cervus rufus : having supernumerary (4th) premolar on one side in lower jaw. HENSEL, Morph. Jahrb., v. p. 555. 362. Ox : supernumerary upper molar on left side. MAGITOT, /. c., p. Sheep: extra molar in left lower jaw, ibid., p. 105, PI. v. fig. 10. [?some error; the figure represents a normal jaw.] The facts given in illustration of Variation in the dentition of Marsupials relate only to a part of the subject and to selected forms. Some of the cases to be given are however of exceptional importance. Evidence is offered in reference to the following subjects:

The following cases of Variation in incisors are all that were met with in the Marsupials examined. I >n>K[,riiYii>.K : incisors normally ;', thus differing from the Dasvuri<l;e (/.',) with which they have much in common1. Of various 1 THOMAS states that the family l>iilel])hyidii' "is, on the whole, very closelv allied to the DaayuridfiB, from which, were it not for its isolated geographical i, it would be very doubtfully separable. " ( 'nt. Mnmtip. lirit. Mas., 1888, p. 815.