vi Journal of Comparative Neurology. 



process. The tube apparently offers less resistance to this stretching 

 process than the nerve does." 



. Allis therefore concludes (i) that the ampullary organs do not 

 correspond to the pit lines of higher fishes, a conclusion that is doubt- 

 less correct ; and (2) that the ampullary organs do correspond to the 

 terminal buds of the higher fishes, a conclusion by no means following 

 from the premises, as I hope to show immediately. 



Now, in the case of Ameiurus I have shown, in a paper published 

 in this Journal since Mr. Allis' work went to press, the presence of 

 lateral line canals and pit lines conforming to the usual teleostean pat- 

 tern, and in addition two sets of sense organs distributed freely in the 

 skin according to no definite pattern so far as determined. One of 

 these comprises the terminal buds, which are strictly typical in struc- 

 ture and mnervation ; the other, a type of small sense organs structur- 

 ally resembling the neuromasts or organs of the lateral line canal sys- 

 tem and unmistakably innervated by lateralis nerves, terminating in the 

 tuberculum acusticum like those for canal organs and organs of the pit 

 lines. The latter organs I termed "large pit organs" to distinguish 

 them from the much more numerous "small pit organs" freely scat- 

 tered in the skin as mentioned above. These small pit organs, which 

 seem not to be present in teleosts generally, may perhaps be directly 

 compared with the embryonic ampullary organs of the sharks, but the 

 terminal buds, never. The argument from the arrangement of the 

 pores of the ampullae therefore falls to the ground. 



Again, the terminal buds of ganoids and teleosts are known to be 

 innervated by visceral sensory or communis nerves, while there is 

 strong presumptive evidence (not amounting as yet to demonstration) 

 that the ampullary organs are innervated by lateral line nerves, a sys- 

 tem which has absolutely no morphological connection with the com- 

 munis nerves. Allis meets this by attempting to show that the inner- 

 vation of the ampullae of selachians is not necessarily the same as that 

 of the lateral line organs and that it may be homologous with that of 

 the terminal buds of higher fishes'. The argument here is involved and 

 rather difficult to follow, but as I understand it, it rests on the assump- 

 tion (a pure assumption with no basis of observed fact) that the ampul- 

 lary organs are innervated exclusively from the so-called lobus trigemini 

 and that this lobe of elasmobranchs is homologous with that of some 

 teleosts, and of Acipenser. These assumptions were suggested by 

 Strong in 1895, ^^^ ^^^ latter one has been given up by morphologists 

 generally, including Dr. Strong himself, if I mistake not, as unten- 

 able. This second assumption grows out of a most unfortunate con- 



