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Show 104 MR. W. BATESON ON [Feb. 2 another would then be manifest. Each . would then have its individual history, just as a Fellowship of a College or a Canonry of a Cathedral has an individual history, being handed on from one holder to his successors, some being suppressed and others being founded, but none being merged into a common fund. In other words, the received view of the nature of homologies in teeth assumes that in Variation the individuality of each member of the series is respected. The difficulty in applying this principle is notorious, not only in the case of teeth but in all cases of Multiple Parts, such as digits, phalanges, &c. ; and when the actual evidence of Variation is before us, the cause of this difficulty will become apparent enough, for it will be found that though Variation may sometimes respect the individual homologies, yet this is by no means a universal rule; and, as a matter of fact, in all cases of Multiple Parts, as to the Variation of which any considerable body of evidence has been collected, there are numerous instances of new forms arising in which what may be called the stereotyped or traditional individuality of the members has been superseded. The present paper concerns the case of Teeth only, and even of this part of the evidence only a fragment can be given in this abstract, but perhaps it may suffice at least to indicate some of the possibilities which are opened up by the Study of Variation. The material examined has consisted chiefly of specimens in the British Museum and the Museums of the College of Surgeons, Leyden, Oxford, and Cambridge, the Paris Museum of Natural History, and several smaller collections. I have to thank the authorities of these several museums for the great kindness I have received from them in the course of m y work ; and in particular I must express my indebtedness to Mr. Oldfield Thomas, of the British Museum, for the constant help and advice which he has given me, both as regards the subject of teeth generally, and especially in examining the specimens in the British Museum. For various reasons I have for the most part limited myself to the following groups :-Primates (excepting Lemuroidea), Carnivora (Canidae, Felidae, Viverridae, Mustelidae, and Phocidae), Marsupialia (Phalangeridae, Dasyuridae, Didelphyidae, part of Macropodidae, &c). Except in the case of teeth which are the terminal members of series, such as the first premolar or the last molar, very few facts of importance concerning the process of reduction in number were seen. From the fact that such cases are generally more or less ambiguous, they must be reserved for fuller treatment. For the present it must suffice to give a brief account of some of the more remarkable phenomena relating to increase in number of teeth. The statistics relate to about 2500 skulls belonging to various orders, and the comparative frequency of supernumerary teeth in some of the different groups is interesting if only from its. paradoxical character. PRIMATES.-Of the three larger Anthropoids-Orang, Chim- |