352 DEEP SEA FISHES. 
For confirmatory instances on bony fishes see Plates LX XI. to LXXXIV. of 
the present work, which represent forms on which the aurals are not con- 
necting and on which subcephalic connections between the system on the 
two sides of the head are generally absent. The facts that the neuration 
of the system on each side of the body proceeds from its own side of the 
brain developing from near the brain to the farther portions in the early 
stages, and that oral, jugular, and, in bony fishes, aural connections are 
somewhat rare, indicate rather conclusively that on ancestors of the fish- 
like vertebrates the lateral system was in two parts, one on each side of the 
middle of the head and the body. Exceptional instances of transverse 
connections in the system are to be seen in the Chimerans, Lat. Canal Syst. 
Plates III. and IV. figs. 2 and 3, where the canals are highly differen- 
tiated, also on the greatly specialized Halieutoids on which the oral is 
continuous from one side to the other, Plates XVIII. to XXV. below, and 
on Chaunax, Plate LXXIII. fig. 1, which apparently has a transverse sub- 
mental series of nerve papille. 
So far as the Plagiostomes are concerned the intention at this writing is 
merely to compare the system in the several species figured on Plates 
LXIX. and LXX. The distribution of the canals on Centroseylliwm nigrum, 
Plate LXIX, fig. 1, and on Jsistius brasiliensis, Plate LXIX. fig. 2, approaches 
that of the simplest arrangement obtaining among the sharks (Antacea). 
Excepting in regard to slight differences in directions and curvatures the 
canals of the mentioned species are similar to one another, with the further 
exception perhaps of the division of the aural (aw) on Centroscyllium, a 
division which may or may not be a peculiarity of the individual corre- 
sponding to that noticed above as occurring on Heptabranchias maculatus. 
In both Centroseyllium and Isistius the median (m) is short and longitu- 
dinal, but on Isistius oral (0) and angular (ang) are more elongate than on 
the other. Neither of them possesses a jugular (7), a gular (g), nor a spira- 
cular (sp), as seen on Chlamydoselachus anguineus, Plate LXX., which see for 
the lettering. On the last mentioned the system was originally traced as 
indicated by the outer openings of the tubules leading from the tubes (Lat. 
Canal Syst., Plate XV.); on specimens obtained subsequently the canals them- 
selves have been followed and sketched, Plate LXX., with a result corre- 
sponding nearly to the arrangement in the diagram first published. The 
median canal (m) proved to be transverse, in this particular agreeing with 
Prionodon Milberti M. H. and with Alopias vulpes Gmel. The functions of 
