58 PROCEEDINGS OF THE ACADEMY OF [1887. 



tions of the larger hair germs, when viewed from the surface. 

 Further study also showed that the rudiment of a hair was Avell ad- 

 vanced in the larger follicles, while in the smaller ones only the first 

 traces of the hair bulb had been developed, without as yet having 

 given rise to the beginning of a cornified hair shaft. In both kinds 

 of follicles the rudiments of sebaceous glands had been developed 

 from the sides of their necks, though a lumen or cavity had hardly 

 as yet been developed within them. The rete mucosum consisted of 

 of scarcely more than a single layer of rounded cells; of this layer 

 the younger developing follicles are principally composed. 



These observations show that there are two distinct types of hair 

 germs developed in the skin of the foetal cat, one of which is much 

 more advanced in development, and far less numerous, at the same 

 period, than the other. It has also been shown that the larger germs 

 have a certain orderly linear arrangement in some regions, as, for 

 instance, along the dorsal region. The questions which now present 

 themselves in addition to the interpretation already suggested, relate 

 to the nature of these different kinds of hair germs. It seemed to him 

 not improbable, as surmised by Professor Leidy, that the larger germs 

 may be those of the contour hairs, while the smaller ones represent 

 the germs of the finer hairs of the under pelt or woolly coat. Yet 

 this view does not dispose of the question raised by the fact of the 

 orderly arrangement of the larger germs along the back ; nor are 

 they numerous enough to be the germs of the contour hairs. It may be 

 that this orderly arrangement relates to an ancestral condition, in 

 which the hairs were fewer and while the ancestral mammalian 

 type was still nearly cold-blooded. This view is supported by the fact 

 that the temperature of the blood of the most reptilian of the mam- 

 malia, viz., the Ornithodelphia, is considerably below that of the 

 Didelphia and Monodelphia, and that in at least one of these forms. 

 Echidna, the spines, which represent hairs, are ai'ranged in rows. 

 In the other genus, Ornithorhynchus, the contour hairs are flat, the 

 Tinder-pelt of avooI hairs being very densely set, while the contour 

 hairs are not. AVhether the quills or spines of Echidna are to be 

 regarded as having descended by development from contour hairs is 

 not known, but it is to be admitted that hairs of that type are most 

 likely to have been developed into quills or spines, since they gener- 

 ally project above the level of the woolly coat and have a much heavier 

 shaft, which is always nearly straight and not crimped. Such an 

 origin may, with much show of probability, be ascribed to the quills 

 of the porcupine. 



