118 



EDWARD PHELPS ALUS, JUN. 



Review and Comparison. 



The lateral sensory canals of selachians seem, at first sight, 

 to have a distribution that admits of but little detailed 

 comparison with the canals of the bon}^ fishes. This differ- 

 ence in detail is, however, largely in appearance only, and 

 not real. 



Imagine the snout of Mustelus pressed backward into and 

 on to the dorso-anterior surface of the head, and the mouth 

 pulled forward until it comes to lie at the anterior end of 

 the snout. What is actually a part of the ventral surface 

 of the snout would then become a part of its dorsal surface, 

 and an arrangement of the lateral canals would arise such 

 as is shown in lateral view in the adjoining cut. This cut 



Fig. 1. 



Side view of an assumed projection of the lateral canals of Mustelus 

 on to the head of Amia. 



represents, in fact, the projection, so to speak, of the canals 

 of Mustelus on to the head of Amia. A front view of such 

 a head would be quite accurately represented in Garman^s 

 front view of Mustelus canis (21, pi. viii). 



In this imaginary head the infra-orbital canal begins on 

 the top of the snout, posterior to the single nasal aperture, 

 find is there in direct communication with the supra-orbital 



