1898] NOTES AND COMMENTS 371 



face, also more slender limbs. Continual in-breeding tends to keep 

 the jaws and face elongated and the limbs slender ; while the 

 frequent accession of new blood has precisely the reverse effect. In 

 connection with this Prof. Branco ingeniously remarks, that in early 

 Tertiary times, when there were much fewer mammals than in later 

 times, in-breeding must have been comparatively common and may 

 thus account for the universal long jaws and numerous teeth 

 characteristic of all genera of the period. 



A second cause of the reduction of the mammalian dentition is 

 the preponderating growth of one or more of its components ; such 

 as the excessive development of the canines in Sus, and of the last 

 molar in Phacochoerus. 



As already long recognised, teeth also disappear when their 

 function is lost. Hence the loss of the upper incisors in ruminants 

 and most of the incisors in elephants, when the tongue and the trunk 

 respectively usurp their functions. Hence also the loss of canines 

 when effective weapons in the form of horns appear. 



Finally, it follows from these considerations that changes in the 

 mode of life and feeding have always been most potent factors, not 

 only in modifying the individual teeth, but also in tending towards 

 their reduction in number and the preponderating development of a 

 few. 



A New Peripatus 



A good deal was said about the Peripatidae in the pages of Natural 

 Science in connection with the publication of the fifth volume of the 

 Cambridge Natural History, and in the series of short articles giving 

 the opinions of various experts on the classification and constitution 

 of the Arthropoda. 1 Since that time the literature of this interest- 

 ing family has been enriched by several papers, by far the most 

 important of which is Dr Willey's memoir on the species he procured 

 in New Britain (see Natural Science, vol. xiii. p. 280). New Britain 

 is an island lying off the east coast of Papua and forming part of 

 the Austro-Malaysian sub-region of the Australian Region of Sclater 

 and Wallace. Hitherto no member of this group had been dis- 

 covered in this area, although several species have long been known 

 from the adjacent sub-regions of Australia and New Zealand. One 

 species too has been recorded from Sumatra ; but some authorities, 

 including Dr Willey, seriously doubt the accuracy of this locality 

 on the grounds that this alleged Sumatran species is apparently 

 generically identical with the Neotropical members of the family. 

 Other zoologists, on the contrary, not unmindful of such facts as 

 the distribution of the existing species of tapirs in the large Malay 

 islands and in tropical America, are not quite so sceptical and see 



1 Vol. viii. pp. 122, 215, and 285 ; vol. x. pp. 97 and 264. 



