664 E. PH. ALLIS, 



Turning now to the lateral canals, the main lateral canal of the 

 head of Pohjodon is a direct anterior continuation of the lateral canal 

 of the body, as Collinge says, but, contrary to what that author 



they resemble end bnds, and his assertion that this has never received 

 confirmation, he can not be familiar with Maltrer's work on "Die Epi- 

 dermis und ihre Abkömmlinge', published in 1895. In that work he 

 would have found the following statements (p. 300) : all cutaneous sense 

 organs "sind stets in ihrem Bau von der einfachsten Form ableitbar" ; 

 (p. 301): "wir müssen aber festhalten, dass sie aus gleichartigen An- 

 lagen hervorgegangen sind"; (p. 301): "alle diese Organe epidermoidaler 

 Herkunft sind"; and (p. 323): "Ich habe Gründe angeführt, die dafür 

 sprechen , dass Endhügel aus Sinnesknospen hervorgehen können." 

 Maurer furthermore says that all the cutaneous sense organs of Am- 

 phibia "stellen niemals Endknospen dar, sondern sind immer und aus- 

 schliesslich nach dem Typus der Endhügel gebaut". If this be so, and if 

 Endhügel und Endknospen be not derived the one from the other, we 

 are led to the conclusion, under Johnston's theory, that a large number 

 of irregularly scattered lateral sensory organs are found in amphibians, 

 selachians and the cartilaginous ganoids, "which have wholly disappeared 

 in Amia^\ together with their related nerves, there being replaced, topo- 

 graphically, by a totally different set of organs and nerves. And John- 

 ston simply says, at least in so far as the selachians and cartilaginous 

 ganoids are concerned, that "there is no difficulty in this supposition." 



As to the possibility of a portion of a certain cerebral center be- 

 coming, so to speak, detached from that center, and then attached to 

 another center, as I suggested ; or even as to the possibility of that 

 detached portion changing markedly in function, which formed no part 

 of mj' suggestion but does form part of Johnston's interpretation of it; 

 we have Johnston's own statements, in his work on "The Brain of • 

 Acipenser", that, (p. 120) "Of these nerves the V is the most constant 

 in Vertebrates, but it has become separated with its sensory nucleus 

 from the central apparatus of the VIII nerve in the higher forms" ; 

 and (p. 186), "In the History of Vertebrates the habenular apparatus 

 seems to have changed its functions. In primitive Vertebrates it served 

 the parietal eye and the olfactory apparatus. ... In the higher forms 

 the ganglion serves as part of certain indirect paths and possibly as 

 an optic center". 



Under all these circumstances it seems to me that I am fully 

 warranted in slightly changing two of Johnston's expressions, and saying 

 that, had Johnston studied the peripheral distribution of the fibres he 

 finds arising in certain cerebral tracts with anything like the care that 

 has characterized his several researches upon those tracts themselves, 

 and had he thoroughly acquainted himself with the structures in the 

 epidermis that those fibres innervate, he could not for a moment have 

 entertained the hypothesis which he tries by a long and laborious ar- 

 gument to establish. 



