260 PROCEEDINGS OF THE CANADIAN INSTITUTE. 



the Siluroids, where the barblets, like the pectinated ridges on the 

 head of Amblyopsis, are little else than carriers of such end-buds. 



F. E. Schulze had already pointed out the difference in form of 

 the sensory cells in these two kinds of end-organs, those of the nerve- 

 hillocks being short and conical in form, while those of the end-buds 

 are long and rod-like. That this difference of form con-esponds also 

 to a difference of function has been rendered certain by the study of 

 the nerve supply of the nerve-hillocks, and many facts point to the 

 truth of Mayser's suggestion that we have in the ' mucous ' canals of 

 the head and of the lateral line with their contained nerve-hillocks, a 

 low form of auditory organ. In describing further on the origin of 

 the nerves distributed to the mucous canals of the head in Amvu/rus, 

 we shall find further support for Mayser's theory. 



This sharp distinction between the two classes of organs does not 

 appear to be recognized by Ley dig, who finds that in the pike the 

 organs of the lateral line and the beaker-shaped organs agree essenti- 

 ally in their structure. My observations on Amiurus convince me 

 that the neuro-epithelium has a very different character in the two 

 sets of structures in that genus. As I have no new details to offer 

 with regard to the structure of the end-buds, I shall only devote a 

 short space to the description of their situation, number and form. 



(a) End-Buds. — End-buds ai^e to be found in profusion in Ami- 

 urus, for tactile sensibility is at its highest development. Not only 

 are they present in great numbers within the cavity of the mouth, on 

 folds of mucous membrane on the gill-arches and on the contractile 

 palate, but the snout and skin of the head, and especially the lips, 

 are thickly covered with them. They diminish in number backwards, 

 and are less frequent on the trunk, as may readily be inferred from 

 their function. They may be most easily studied, however, where 

 they reach their greatest size, and are most closely crowded together, 

 i.e., on the barblets, which are solely for the purpose of increasing the 

 functional range of the end-buds, and are little else than modified pro- 

 jections of the skin stiffened by a cartilaginous axis attached to under- 

 lying bone, and bearing on each papilla an end-bud. There are eight 

 such barblets in Amiurus ; the 'nasal' project upwards in front of the 

 posterior nares, and are supplied by a large branch of the R. ophthal- 

 micus profundus. The ' maxillary ' are the largest and most freely 



i Zeit. fur wiss. Zool. XXXVI., 312. 



