572 DBS. GEOBGE ATfD rEA:N'CES E. HOGGAK OK 



The different elements on the two structures seem to accord so 

 perfectly, that the wonder is that no one should have previously 

 observed the identity between them. The identity might, how- 

 ever, have been suspected, although, the knowledge of the cha- 

 racter of the nerve-elements being very recent, it would have 

 been impossible without it to have demonstrated that identity. 

 "We have to remember that it was only in 1878 that the forked 

 terminations on the hairs, the homologues of the most prominent 

 elements in the organ of Eimer, were discovered ; and we our- 

 selves are now demonstrating for the first time the existence of 

 nerve-cells on ordinary hairs and their peripheral continuations 

 (figs. 7 and 15), which represent the fibrils af the centre group 

 proceeding from the nerve-cells at the base. 



At the time when Mojsisovics, who has made the most complete 

 inquiry iuto the character of the organ of Eimer, published his 

 researches in 1876, neither the forked terminations nor the nerve- 

 cells with peripheral fibres were known ; and as these really form 

 nine tenths of the organ, it need be little wonder if he failed to 

 observe an identity between it and the hair-follicle. 



The nest question is the very interesting one of how the Mole, 

 and the Mole alone, came to be possessed of so unique and 

 peculiar a nerve-terminal organ on its snout, and upon its snout 

 only ; for on the under lip we have only the ordinary intraepidermic 

 fibrils as they are seen on the lower lip of other mammals (if, 

 fig. 25, Plate XVI.) . A very little observation of the peculiar habits 

 of the Mole will enable any one, we think, on reflexion to under- 

 stand one of the prettiest lessons on the effect of habit in 

 causing the evolution of what at first sight may appear to be 

 strange and unique structures, microscopic in size, and conse- 

 quently less tangible than, for example, the alterations in the 

 fore paws of the same animal. 



Eff^ect of Habit in causing Evolution of Organ of Eimer. 

 Atij one who has watched a Mole digging into earth, and noted 

 the energy and force with which it uses its powerful hands and 

 the direction in which they are moved, must liave felt that if 

 the animal were suddenly provided with a set of feelers like a 

 mouse or rat, these would be certainly torn out by the roots by a 

 few powerful strokes of the digging hands. Such has evidently 

 been the case in the remote past with the hairs on the extreme 

 point of the snout of the ancestors of the whole Mole family ; and 



