THE LATERAL CANAL SYSTEM. 363 
of which, indicated in the sketch, is continuous with the lateral line of the 
body and another apparently with the cranial canal of the head; and no 
disks appear to be developed on the body. 
Merluccius angustimanus and Phyciculus rastrelliger, Plate LXXXII., are 
diverse forms which probably are not well placed in the same family. Both 
are Gadoids but IZ. angustimanus exhibits a lateral system that differs con- 
siderably from that of its nearest allies in the Gadide. Compared with 
them the arrangement is similar, there are no frontal branches of the cranial, 
and there are two disks in each aural, but it is in peculiarities of the disk 
that the differences appear. Each disk is a broad band-like mass of tissue 
on which there is a thin yellowish cover apparently granulated on the sur- 
face and thicker in the middle, between the ends of the connecting threads, 
in the position of the centrum. The centrum is not well differentiated, 
though the glandular mass, in greater depth at this point, probably answers 
its purpose; the fusiform portion of the disk was not to be detected. The 
linings of the canals are pigmented, which with the lack of concentration of 
the glandular tissue in a centrum may indicate differences in function. 
There are 54 cephalic disks. The disks of P. rastrelliger are like those of 
other Gadide ; they are small, nearly uniform in size over the head, and 
each aural, with two disks, turns sharply forward. The specimen possessed 
66 disks on the head. 
Microlepidium grandiceps and Maerurus anguliceps, Plate LX XXIII. repre- 
sent allied families which differ in regard to the amount of dependence placed 
on the lateral system. JZ. grandiceps of the Gadidee was taken at the greater 
depth, 1421 fathoms, but has less development in the disks, which are 
small, and nearly uniform in size. Postorbital and spiracular series are 
brought rather close together in this species; no frontal branches were dis- 
covered; there are two disks in each aural branch and 62 in the entire 
cephalic portion of the system. In Macrurus anguliceps it is evident that 
the function of the system is of more importance; it has attained a much 
higher degree of development, though the species was taken at a less depth, 
1067 fathoms. The minute disks in the frontal region illustrate the manner 
in which as some of the disks increase in size their number is reduced, some 
of them growing larger, others gradually disappearing. Including the obso- 
lescent, there are 72 disks on the head of this species. On one of the spe- 
cies on this plate the eye appears to be developed far beyond the system ; 
on the other, eye and system are about equally important. 
