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

As will be shewn in the next section, absence of the front premolars is a common character in the dogs of the ancient Incas, but in them the posterior molars are also frequently absent. There is no special reason for supposing that the Esquimaux dogs came originally from America, but it may be worth recalling as a suggestion, that according to anthropologists the relations ut thf K-i|iiimaiix anrather with American tribes than with Kiirup.-.-ins Jt' this were established, it would be not unlikely that tin- Ks<|uinmux dogs might be descended from dogs domesti- • 'I in AimTK-a before the coming of Europeans, and so far belong ratlin- \\ith tin- Inca dogs than with ours1.

*244. Inca Dogs. The domestic dogs from the Inca interments, belonirinfn a period befontli«- <• ..... ing of the Spaniards, have bci-n in\r~t i»;it»-il I iy Nr.iiKiXfJ. Of nine skulls not one had the full numln-i- "f t'-'-th and th«-n- was no case of supernumerary teeth. Sometimes tinanterior premolar was absent, sometimes a posterior molar, and in some cases both. The formuhe were as follows: I In- di.LfN \M-I-P all of moderate size, and none shewed any defects in tin- t'iii-iii nt1 teeth, which were all strong and sound. XEIIIUXG, A..

*24">. Dog: lar^'- breed. Jn the upper jaw on both sides the third premolar, in-trad <if ha\-ing only two muts has a third internal root, thus Miiiii-wli.-it i-.-<i-inl,lintin- i-arnassial. The crown of the tooth v.-ry >li-hrly ch;inL.'ed. This is nut a case of persistent milk-tooth, which though ,-i three-rooted tooth, i.s very ditren-nt. C. S. M., 55s. Supernumerary molars an- m.t i-anin Cauida.-. In all cases seen by me these teeth are siiigl.-rooti.-d, round-crowned, ratlin tubercular teeth, plan-d behind >»- or "^ as the case may be. Hi \>i.i.' haobserved that it' „,> occurs, thru ,„* which is normally single-rooted, not iiinv(|urnt l\ has ;l ,|uul»lc rout, i hough the same variation may occur when there is no m* promt. CUM vn-M-ly, u1"'" "- is absent, nut a raiv \ariation, then ^ is often of a

aon ' wolves, an.l aaya th.-a th.-v ot'tn; breed with tlir \vulf P Z S size below the normal, having a single root and a crown slightly developed, like that of m3. This reduced condition of „,- may also occur in cases in which „>'•' is not absent. These observations of Hensel's, which are of great consequence to an appreciation of the nature of Repetition, I can fully attest, and similar cases of Variation in adjacent teeth associated with the presence of a supernumerary were seen in other animals also.

246. C. lupus: 26 normals seen. Specimen from Courland having supernumerary m? on left. In this specimen «^ is rather abnormally large on both sides, and the lower third molar, on the left side, viz. that on which the upper jaw has an extra tooth, is larger than right ^, but it is not larger than usual. C. M., HENSEL, 1. c., p. 548, saw 27 skulls, none having extra molar, but one specimen known to him had a right w^. The S. American Camdce (Lycalopex group) are remarkable for the frequency with which they possess extra molars, as the following cases (C. azarce, vetulus, magellanicus and cancrivorus) testify. FLOWER and LYDEKKER1 speak of the occasional presence of w3 in C. cancrivorus, but the evidence taken together seems rather to shew that there is a general variability at the end of the molar series in both jaws in these species ; for not only is ^! found, but in some cases m* also, while in one instance there was an 'odontome,' or rather a complex of 4 small teeth attached to m3.

248. C. vetulus, Brazil : specimen having an extra molar in right lower jaw (Fig. 44, 1.). The posterior part of m? is slightly pushed outwards and a very small extra tooth stands behind and partly internal to it. Right Irf is slightly larger than left m? and differs from it also a little in pattern. The extra tooth has one large and about three smaller blunt cusps on its crown, and might be described as a small representation of the larger w* seen in other cases. B. M., 84. 2. 21. 1 (mentioned by MiVART2, Monoyr. Canidce). *249. Canis azarae : Brazilian specimen having a large sup«T- numerary molar («&_3) in each upper jaw placed in series with the others. In this specimen the great enlargement of ^ is very

- In the same place Mivart mentions a case of wf in " C. cancrivorus," Imt I have not seen it. Perhaps this reference is to van der Hoeven's case (No. 24U) which was by Burrneister named C. cancrirorus (see HUXLEY, P. Z. S., 1880, p. 2(>s). on both sides, and this tooth is present as a large tooth with apparently three roots. In the lower jaw there is noextr.-i li, lint the molars are considerably larger than those of a ;:;. < -HIM azara . I. :m.l II. Itight upper and lower jaws of the specimen • !• -i-i il>i d in N". -Is. s-licwin/ tlie extra upper molar and the correlated enlarge- ' ' . III. ami IV. are taken from a normal specimen of slightly

normal speeimrn < Kig. 4o ). In the figure, side by side with the ;<•>•! h ut' tinalnioniial form. anshewn the teeth of a normal skull whieh w.-is -.lightly larger than the abnormal one, for comparison. C. cancrivorus. The ..uly -kulls of this species seen by me are those in I',. M. < if these «n<- ^kull with lower jaw, one skull without l<>\\er ja\\ . .-iiid one lower jaw without skull, ha\e ninnerically the noiinal dentition nf Cants, Init of these, one has ri^ht m8 much larger than corresponding left looth. The following were abnormal: small tuliereiilar m* on l.oth Cities, u]']ier series normal, I!. .M., 1033, l>, and also 15. M.. 1033, C, (Fig. t I. 11.) mentioned l,y H t \i.i;v, ' I. c.

Specimen haxini,' upju-r series and left lower series normal. On inner -ide of ri^ht „, and as it were ^rowin^ out from this tooth is a large 'oclontome' composed of four small tubercular teeth. Eacli of these has a distinct crown and neck, but apparently the necks join with FIG. 44. Posterior lower molars of S. American Foxes. I. C. vetidus No. 249. II. C. cancrivorus No. 251. III. C. cancrivonis No. 252. In each case the right and left sides are shewn. R, right. L, left.

each other and with the neck of ^, which is displaced (Fig. 44, III.). In answer to an inquiry, Prof. NKHRING informs me that he has three skulls of C. cuiicrivorits Desm. ( = C. bruzilienais Lund.) from the province of S. Paolo, Brazil, which are normal, except that in one pi has never replaced &, which is in place ; and that another Venezuelan skull of this species is also normal. [Whether the B. M. specimens are really of the same species as these I do not know.]

The rarity of supernumerary molars in C. vulpes, the common Fox, is remarkable in contrast with the foregoing evidence, In 142 cases (to which I can add 37), HENSEL, Morph. Jahrb , 1879, found no single case. »*•- is very rarely absent in Canidse, and among the wild forms no case~seen in 289 skulls (except a doubtful case in C. occidental is, right * It is remarkable that in each of the two genera Icticyon and <>(,,<• I/mi, whieh are especially distinguished from Canis by the possession <>t unusual dental formula-, numerical Variation in the Th has been recorded, though the number of skulls of these forms in Museums is very small. The two forms, besides, differ fr<>ni Canis m opposite ways, the one having a tooth less in each jaw \\hile the other has in each jaw a tooth more, so that the pi* -ei ice of extra teeth in the two species is all the more important.

255, Icticyon venaticus : according to the authorities has p±, m^, vix. a nn .lar less than the Dog in each jaw. The following skulls are all that T have seen. The carnassials did not vary appreciably in tintlm-r skulls. Kai-li --kull differs from the others, as follows. 25li. Otocyon megalotis [^ /nf<!n<l!i and en for]: the usual formula isy[, />< y. that i-. niir molar more than the Dog in each jaw. It occurs in I >kulls at I!. .M . and in 2 at C. S. M. One specimen has in addi-

tion an extra molar of good size in each upper jaw, giving m - 2">7. Dogs. In :H") skulls the following i'S ,-;lSes occurred, chiefly in large breeds : This was the only case in 860 skulls of Canis, of which about 650 were Dogs. The formula in it is thus that of Otocyon or the fossil Aiaphicyon. NEHRING, Sitzb. naturf. Fr. Berlin, 1882, p. 66. In 216 skulls seen by me there were 8 cases of extra molars, viz.:— FIG. 45. Posterior molars of lower jaw of Mastiff No. 259, having an extra ,„< on the right side. Right m3 is materially larger than left ^3.

260. Dog, large size, supernumerary w4 on right side. On both sides m? is two-rooted1 and of large size. Letjd. J/»s., 258. 261. WIXDLE and HUMPHREYS, P. Z. «S'., 1890, p. 27, give an account of extra molars in the Dog, speaking of upper jaws only, and some of the foregoing are mentioned by them. As they do not specify the collection in which each is found the identity of the cases is not easy to tell. The following cases given by them are, I believe, all in addition to those already specified : — Bulldog, Lurcher, Pointer and Terrier, »^ on both sides. Bulldog »»3 on left side; Esquimaux, Pug, Spaniel, West Indian Dog, »<_3 on right side.

9(32 D°S : ui 345 skulls the following seen : m* and ^5 absent on both sides, 2 cases ; " ^2 and ^ absent on both sides, 1 case ; /^ absent on both sides, 25 cases ; ^ absent on one side, 9 cases. HEXSEL, I.e. 1 It generally has a simple, conical root, but not rarely it has an imperfectly divided root, <>.//. Newfoundland dog, 0. M., 1778. Inca dogs : for evidence as to absence of molars, see No. 244-. Th.' follow ing evidence relates to the genera Felis and Cyncelurus. 'I'll" usual formula is ,§, cj, ;?f, w{. Of wild species, •27s- adult skulls having no extra teeth were seen, and s eases ..f extra teeth (nearly 3 per cent.): of domestic Cats, 35 adults \\ithout, and 3 cases with extra teeth (so far, about i) per cent.). A- in Canidasu in Felidw, there is a remarkable group of cases ot' \ariation in the anterior premolars. In the normal a small anterior pivmolar stands in the upper jaw, and commonly it is one-rooted, sometimes two-rooted (cases given); but there is no <mall anterior juvniolar in the lower jaw.

Cases ot variation consisting in the presence of tw<> small pr.-molarab..ve are common1, just as there are often two small anterior preniolai> in the Dog. There are besides a few cases nf tinpre-enee nf a small anterior premolar in the lower jaw, Inn they are rather rare, and curiously enough there seems to he IK. case of the e, .1 1 icideuce of these two variations in the same 3kull. A- already Dialed, in describing cases, the small anterior preinolar in the upper jaw will be here spoken of as /^, though no suggestion that it is the hoiuologue of the Dog's ^ is meant.

In a few speeies />l is UK.-) commonly absent (cases given). There are some rurious cases ,,f i/n^h'n/tes of large premolars (Cat) and one of tl'ijJ/i'iite cmiim- (Tigei1), also a few of supernumerary molar. TliMii-h BO small, and liitinmi no tuoth of the lower jav. - nearly always in place even in old skulls (HEXSEL). NI. quite satisfactory case "f nunicrical variation in incisors of Felicia known to inc. The t'olluwiii -lii.iiM liDWi-vcr l.c i.'.ciitiniicil.

F. pardalis: '' and ,i ul.seiit on left side. A- i.-ards the lower jaw the tooth ;;/•/// have t.eeii jircx-nt. and I., en lost, but left /' has probably never been present. It is e-|.i cially notable that let't '' is larger than ri^-ht ^, but there is no indication that i'1 is coni|.ounded \\itli it. II. M., lOt'.s, ,/. ->i;- Cync-rlurus jubatus : no trace of ik'ht P; same skull has no )^; lower jaw ~2ou. F. pardus : right 7'1 single and normal; on 1. side two such teeth, both standing at level anterior to right p1. The anterior is of same size as right .2^, the posterior is rather smaller. B. M., 87. 4. 25. 1.

2b/. F. eyra : two small anterior premolars in left upper jaw, BAIKD, U. S. ami Mi'.r. Bouinl. Knrv., Pt. 2, PI. xm. tigs. 2, a and 2, c [anomaly not mentioned in text]. *268. F. catus, Athens. Two small anterior premolars in upper jaw both sides (Fig. 46, I.), small and standing close together. On rt. anterior the larger, on 1. posterior the larger. B. M., 47. *269. F. inconspicua (= torquata). Rajpootana. Two small anterior premolars in upper jaw both sides ; both small, diastema between them. Posterior is nearly in contact with ";/", while anterior is only a little behind canine (Fig. 46, II.). B. M., 85. 8. 1. 26. (Another specimen has p^_ as large single-fanged tooth.)

270. F. domestica (out of 38 skulls): internal to and rather behind left P^ is an almost identical copy of it, though rather smaller. Not a milk-tooth. C. S. M., 414. 272. r- caligata, Socotra : outside right p^, a small extra tooth. In this specimen f^ on each side has two roots. B. M., 857, b. Doubtful cases of extra upper anterior premolar, F. pardus, C. S. M. 365 ; F. leo, F. concolor : a supernumerary anterior premolar on both sides present, Berl. Anal. Mus., 3G78. HEXSEL, ibid. F. catus or maniculata : ditto. Frank/. Mus., HEXSEL, ibid. F. catus : ditto, on left side, closely resembling pl. Two cases, B. M., 1143 and 1143, «.

F. domestica : (in 252 skulls) a supernumerary premolar on both sides, just in front of and nearly same size as the usual "P~_" one case ; on left, as a very small tooth midway between canine and "p~*," one case ; on right, rather larger than in foregoing and nearer to "p," one case. HEXSEL, ibid. 275 F. tetraodon: alveolus for small anterior premolar in right lower jaw; but as this fossil form very rare, uncertain whether normally iinaiily lai^'e, left normal. Minute alveolus external and posterior

mi 1> ft .-Mi- a small worn stump [? of milk-tooth] in this ahvolus. In tht.- following cases it appeared that ^ hud not been present. Iii thr following species the absence of ]^ was so frequent as to call fur ^pci-ial not iff. 071, Cynaelurus jubatus : of 8 skulls 3 (2 African) were like Cat, iniu'lit have liffii present, and in these it was doubtful. •_'M. Lynx: ut' Lynxes of possibly different spcfics, 17 skulls have no p^, 2 si'. F. pajeros ( pampana), Chili: i' skulls only known to HKXSEL, '. c., l.otli without p\ 'I'l'is tooth absent in B. M. 126 and 126, c; but in uiif sjiffinifii seen, ri^ht y' absent but left /^ of good size.

Two cases ivl.-it.- to this subject. The first lower ])reinolar "t FelidaB is a two-rooted tooth of well-known form. In the first of tintoll, .\\in-- cases it boiv an extra talon and root; in the sffond tli.'iv \\.-is a Mnall t-xtra root ,,n the internal face. (Cp. C. vulpes, No. -2'-\d) P. tiglii: anterior right Lower premolar has a thin supernumerary root on intfi-nal uide of' thf tooth at the level between the two normal roots. Thi> loutli iii f-.i-m iv-fiiiblfd a niilk-farnassial to some extent, but it was ft-rtainly not one of the normal milk-ti-eth. C. S. M., 333.

*2S4. F. fontanieri (see No. 290) : anterior premolar of right lower jawhas additional talon on internal and anterior surface (Fig. 47). This A. The normal anterior prernolar of the left lower jaw. B. The corresponding tooth of the right side from above. C. The same from the lingual side. portion has a separate root, and stands somewhat apart from rest of crown, looking like a partially separated tooth. B. M., 90. 7. 8. 1. 285. F- tigris: on right side, two canines in the same socket, both of large size, the anterior being the smaller; neither is a milk-tooth. Mus. Odont. Soc.

286. F. domestica : having a large supernumerary tooth in each upper jaw. The extra tooth was in each case a small but accurate copy of the carnassial tooth (Fig. 48) of its own side. In each case the extra tooth stood internally to the carnassial tooth, extending from the level of the middle of the carnassial tooth to the level of the middle of the molar. B. M., 83. 3. 10. 1. 287. Specimen having a tooth in the upper jaw closely resembling the second premolar ("p3" auctt.} internal to and between it and the carnassial. The internal tooth is slightly smaller than the second premolar1 (Fig. 49). C. S. M., 414.

1 In this case, it is not possible to say strictly that either of the two teeth " is" the normal second premolar, rather than the other. 288. Specimen having a small tooth internal to the middle of the lower [?sid. cafnassia] < • ): the extra tooth was here divided into two cusps so that it was a copy of the carnassial. HEXSEL, /. c. i. -10. Plan of teeth in upper jaw of Cat, No. 287. The two teeth marked with crosses are separately shewn, that on the right being the external.

2s!». Specimen having a tooth like the last, but not so distinctly divided into two cusps, internal to posterior end of lower carnassial [?side]. ibid. Cases like the last cannot be clearly separated from cases of true extra inulars in scries, such as the following. It is remarkable that no case of supernumerary upper molar in series seems to be known in Felicia?. In the Tiger and other species the upper molar is sometimes single- and sometimes double-rooted.

F. fontanieri : a species nearly allied to the Leopard (F. y»//v/'/M, inhabiting the Kiu-Kiang, a geographically isolated region of N. ( 'hina. Only t\vo skulls are known, and each of them presents an abnormality in dentition (see No. 2N4). Skull having >npei nuinerarv tubercular tooth in series (m*) behind the left lower molar (j/T1). B. M., 14!K), a. F. leo : '"' ali-mt on botli sides, and tliero H m> s]iace for it behind the upper cnrnassials. B. M.. :<ui:i. Tlie only case set n in all Fuliclaexamined. F. domestiea : '»' absent [? both sides]. HEXSEL, /. c., p. 541.

Of the Viverrida?, Herpestes and Crossarchus are the only genera represented in collections in quantity sufficient to repay study of their dental variations. In the teeth of these two genera, however, variation is considerable and appears in some interesting forms. In Herpestes there is first some evidence of variability in the number of the incisors, including one case of extra incisor. Next the facts respecting the presence or absence of the anterior premolar are of some consequence, both as illustrating the general variability and modes of Variation of this tooth, and also because the normal presence or normal absence of the anterior premolar is one of the characteristics of different species, which shew a progression in this respect. There is one case which should probably be looked on as an example of duplicate anterior premolar.

There are besides two cases of duplicates of large premolars, but of true supernumerary molars in series only one case was seen. Another specimen shewed what is perhaps partial division of a molar. Of 130 skulls, five had supernumerary teeth, not including cases of unusual presence of anterior premolar. The following cases shewed departure from the normal i'±. 292. Herpestes gracilis : an extra incisor in lower jaw. ~fi and P in place and clearly recognizable on both sides, but between the two second incisors are three small teeth, all of about the same size and shape. Neither of these is a milk-tooth, for the milk-teeth are distinctly different both in size and form. There was no evidence to shew which tooth was the supernumerary one. B. M., 826, a.