THE LATERAL CANAL SYSTEM. 359 



they are covered effectually ilirects the function downward through the 

 opening- at the lower edges. In some types the scale on which the disk is 

 borne has become so enlarged as to lose its position and identity with others 

 about it and to appear as if a superficial and accessory acquisition. There are 

 such acquisitions outside of the disks, however, on LamprognMnmus. On 

 the body of Phi/cis ret/iiis and on the top of the head of Halosauri the system 

 appears to be more primitive in character than on other portions of the 

 body. 



If in its inception the Lateral Canal System was tactile in function there is 

 no evident reason why, in the complete darkness of the abysses, more than 

 ever before demanding its exercise, this function should deteriorate or be 

 lost; but instead all the circumstances would appear conducive to its en- 

 hancement and perfection. Unless something better has been substituted 

 for it, it is likely that the tactile function has been retained in the lateral sj's- 

 tems of all of the bathybial fishes. That the additional and very complex 

 apparatus present on some species is to subserve the same purpose and 

 nothing more is not so likely. Structure, pigmentation of adjacent tissue, 

 apparatus for hiding effects or for controlling their directions, considered in 

 connection with the absence or the presence of the eyes and their develop- 

 ment, the character of the bathybial light and the probability of incursions 

 into profound darkness all tend to make the conclusion unavoidable that the 

 tactile organs of the lateral sj'stem have in the great depths become lumin- 

 ous organs also, and that on many species they are so controlled by their 

 possessors as to answer the purposes of flash organs. Again, the possession 

 of apparatus in the disks beyond the needs of mere light organs, by blind as 

 well as by eyed forms, indicates that there is yet more than the tactile and 

 the luminous to be accounted for; and in these cases we are apparently 

 driven to conclude that electric functions exist, functions by means of which 

 the species or the sex of the individual is recognized, the members of the 

 school are kept together, and by means of which the prey is captured and 

 the enemy is avoided. A probable addition to the functions of the lateral 

 system is the sense of taste ; the sen.se of smell is otlierwise provided for in 

 well developed olfactories. 



In the Bulletin of the Museum of Comparative Zoology, 1888, Vol. XVII. 

 p. 72, an attempt at the use of the lateral system in classification was made 

 by the writer. In this essay special stress was laid upon the arrangement, 

 connections, branching, etc., for the separation of species, genera and higher 



