308 



dispirema, di cui parlauo questi autori, non sia altro che la fase a 

 gomitolo che segue la sinapsi, sembiano parlare in quel seuso. 

 Ma appunto Tiusieme delle altre osservazioni fa sorgere molti dubbi 

 suUa verita di quel risultati, e rendono difficile ammettere che 

 in quegli animali si Dfiantenga per tutta la vita delFoocite la indivi- 

 dualita dei cromosonii e non si formi il reticolo secondario caratteristico 

 degli oociti. 



Palermo, 21 febbraio 1902. 



Nachdruck verboten. 



The Homology of the Selachian Ampullae. 



A Note on Allis' recent Paper on Mustelus laevis. 



By J. B. Johnston, 

 Professor of Biology, West Virginia University, U. S. A. 



In his description of the cranial nerves and sense organs of 

 Mustelus (2) Mr. Allis makes an argument to show that the nerve 

 sacs of ganoids and the ampullae of selachians are ^the homologues 

 of the end buds of teleosts, rather than of the lateral line or pit or- 

 gans. This argument appears to me wholly unsound and likely to 

 lead to further difficulties in a matter which the work of several authors 

 during the last three years has just redeemed from great and needless 

 confusion. 



The argument which Allis brings forward has four supports: 1) 

 the possible or assumed homology between the "lobus trigemini" of 

 Acipenser and selachians and a part of the fasciculus communis center 

 in teleosts; 2) the presence of fasciculus communis fibres in the oph- 

 thalmic nerves in Amia; 3) the homology of most of the pit organs 

 in Amia with canal organs in Mustelus, so that the ampullae have no 

 apparent homologue in Amia and teleosts unless it be the end buds; 

 and 4) the absence of end buds on the head of Mustelus. 



Let us examine the parts of this argument in reverse order. The 

 last is the least important. Allis made no search for end buds and 

 even if none were present this fact would be of no value in establishing 

 the homology of ampullae with end buds. The number and distribution 

 of end buds on the body of fishes varies so greatly that their absence 

 from the head in any form would not be a matter of great moment. 



The fact that Allis is able to homologize the lines of pit organs 

 in Amia with enclosed canal organs in Mustelus is likewise of little 

 value as positive evidence. The number of lateral organs is so enorm- 



