iniO.] Microgale more Primitive iJuin Potamogale. 237 



paracone of nonnal tritubercular molars, that their true protoconc is the 

 vestigial internal basal ledge, and that they have been derived from a type 

 of molar rcpresented in Potamogale. 



The important monograph of Leche (1907) brings nmcli new evidenee 

 from an entirely dift'erent source to bear upon this still very difficult problem 

 and seems to favor the contrary view that the Potamogale molar is, after all, 

 the derived or i)seudotritubercular type, and that the main internal cusj) in 

 the Centetes molar is homologous with the protocone rather than with the 

 paracone or para + metacone of normal tritubercular teeth (Fig. 1 7) . Leche's 

 work (1907) shows that the problem of the origin and cus{)-homologies of the 

 Centetoid molars cannot be solved through the consideration of dental 

 characters alone, but only by careful study of various parts of the ortTanisni 

 througliout the series, with the view of discovering the general trend of 

 evolution of the forms in question. 



According to Leche's view, the most primitive member of the Centetidte 

 is the minute shrew-like form Microgale jyusilla. The genus Microgale 

 includes some ten species, all of small size, of which some are more adapted 

 for digging, others, with elongate hind limbs and tail, for hopping. In 

 M. longicaxKlata the tail is very primitive in that it is covered with slightly 

 imbricating scales arranged in whorls between which short hairs project 

 (Dobson). In Centetes the tail is lost. In Microgale and its allies the hairv 

 covering retains its primitive undifferentiated form, whereas in Ericulus and 

 Centetes it develops defensive spines. Through the larger intermediate 

 forms M. cowani and M. dohsoni, Microgale foreshadows the obviously more 

 specialized Oryzoryctes, Limnogale, etc. The adult Microgale retains a form 

 of skull displayed by the embryo Centetes, and the nasals remain separate 

 even in old animals, whereas they very early coalesce in Centetes. The 

 fourth digit in the pes is the longest {cf. Marsupials). The so called epister- 

 num, the monotreme-like nature of which was noted above, is preserved, 

 whereas it is much reduced in Centetes. The number of dorso-lumbar 

 vertebrne (usually 21-22) is nearer the primitive number, 19 or 20, than it is 

 in Centetes (23-24). The milk dentition persists into the fully adult state 

 as in the Oligocene Leptictidae (p. 2G0) and certain other Insectivores. 



The female generative organs are as in Centetes, but in the male the testes 

 have begun their descent and lie in the pelvis (Dobson, 1883, p. 86). This 

 is one of the few characters in which Microgale has progressed further than 

 Centetes. Microgale longicaudata and dohsoni retain a free os centrale carpi 

 but in M. cowani the scaphoid, lunar and centrale coalesce. The tibia 

 and fibula have also fused distally, whereas they remain free in Centetes. 

 Leche (1907, p. 41) holds that Microgale is equally primitive in its denti- 

 tion {cf. our Fig. 18, B). In the smaller species the upper incisors, canines 



