458 Edward Phelps Allis jr., 



thus evident tliat the almost complete- enclosure of the canal in the 

 bone, shown by Cole and Johnstone, is secondary, exactly as the en- 

 closing of the same section of the canal in this same bone has already 

 been shown to be in Ameiurus. 



The other canals in Pleuronectes, and also the significance of the 

 presence, in the frontal, of a sense organ of the infraorbital line, 

 will be discussed after the canals in Hippoglossus have been described. 



Hijppoglossus vulgaris. Traquair [70J has given the general 

 course of the latero-sensory canals in this fish, and also their general 

 relations to the cranial bones, but he does not give the number and 

 positions either of the primary tubes or of the sense organs. 



A series of sketches that I have, made in 1887 — 88, give the 

 primary tubes and the numerous surface pores of the system, as well 

 as the general course of the main canals, but they also do not show 

 the positions of the sense organs, which is of primary importance. 

 I have accordingly had dissections made of the fish, in my laboratory 

 here, in order to determine the positions of those organs that I con- 

 sider of importance in the present discussion, and also to control the 

 course of the canals and their relations to the cranial bones. 



The primary tubes of this fish undergo repeated dichotomous 

 division, much branching dendritic systems, with numerous surface 

 pores, thus arising: but, contrary to what is found in the other fishes 

 that I am familiar with, the branches of these dendritic systems 

 lie, in almost every instance, wholly in the dermis, the related bones 

 enclosing simply the unbranching trunks of the systems, or the half 

 trunks resulting from a first dichotomization. 



The main infraorbital canal of the ocular side begins (fig. 30), as 

 Traquair has stated, antero-ventral to the right eye, and from there 

 encircles the ventral and posterior margins of the eye, traversing a series 

 of small tubular ossicles, not shown in the figure. There were eleven of 

 these ossicles in one of the specimens dissected and nine in another, the 

 dorso-posterior ossicle being, in both specimens, somewhat larger and 

 stouter than the others. This latter ossicle is, in position, the dermal 

 postfrontal of the fish, and the innervation, in Pleuronectes, of the 

 organ it encloses, by the first branch of the outer buccal nerve of 



