354 DEEP SEA FISHES. 



tions of tlio fusiform glandular disks at the outer extremities of the 

 nerves. 



An aiiparent depai-ture from the common arrangement is that on Ilalo- 

 saurus radiatus, Plate LXXXIV. figs. 3 and 5, but the difference is in the 

 details rather than in the general plan, for though cranials, aurals, post- 

 orbitals and spiraculars are perhaps without the glandular organs the 

 canals are present and the minute nerve endings no doubt have their ordi- 

 nary tactile functions. The most divergent feature in the system in this 

 case lies in the backward extension of the oral in a short series of glands, 

 sinn'lar to what obtains on Chaunax'and corresponding to the canal on the 

 Antacea known as the jngular, Plate LXX.y. On Halosaurns there is a 

 further variation under the snout ; and on Chaunax while the aural appears 

 to be rudimentary there is an apparent connection between the rostral 

 canals across the snout, the orbital is produced backward on the cheek to 

 the spiracular, the latter is continued downward to the posterior extension 

 of the oral which is continued still farther back toward the base of the 

 pectoral, there are two connections between the oi'bital and the oral, the 

 anterior being the angular {(uig), and there is no postorbital. If it were 

 not for the position of the vertical series on the cheek of Chaunax, so far 

 backward from the orbit and behind the angular, it might be taken for the 

 postorbital while the jugular extension would answer for the spiracular. 



In addition to the variations in the Lateral Canal Sj'stem resulting from 

 changes in the structure of parts of the fishes' bodies adjacent to it there are 

 others, consequents of changes in function ; as on Plit/cis recjiiis, Plate LXXXI. 

 fig. 2, on which the system in the hinder portion of the cranial region has 

 become rudimentary, probably on account of the acquisition by the species 

 of an electric faculty. In this species the canals on the top of the head 

 backward of the orbital are all affected by the change, and the origin of 

 the shocks given by this fish may perhaps be traced to the aural portion 

 of the head. Halosaurus also is a pertinent instance, since the system on 

 the upper half of the head, where the nerve papillae (disks) are insignificant 

 in size or invisible, apparently has the ordinary function of that on the 

 head and body of a fish of the shoals, while in the canals of the lower half 

 of the head the glandular organs are highly differentiated and evidently 

 have taken on the office of luminous bodies and of flash lights. 



One of the most obvious modifications obtaining on bathybial fishes is 

 that taking place in the organs at the ends of the nerves of the Lateral 



