224 JOURNAL OF COMPARATIVE NEUROLOGY. 
homolgy of certain branches of the infra-orbital canal leading 
out to pores with pit lines in Amia is insecure ; for (in. addition 
to the objections raised by ALLIs, ’97, p. 629) these pit lines 
are innervated in Amia by branches of the r. hyomandibularis, 
and not by the r. buccalis, as they should be, if they belonged 
to the infra-orbital series. 
A detailed comparison of the lateral lines of Ameiurus and 
the siluroids described by PoLLarpD is hardly necessary here, as 
the salient features can be gathered very readily by a comparison 
of our figures. Such a comparison, however, brings out very 
clearly the peculiar and intimate relation existing between the 
canals and the dermal bones of the skull, a relation which has 
been recently emphasized by several writers. It is manifest 
that many of the bones, such as the extra-scapular and the sub- 
orbital series, have been developed for the canals. Conversely, 
it is equally evident that the canal is toa large extent depen- 
dent (probably as a cenogenetic adaptation) upon the bones 
and tends to disappear in their absence, as in the case of the 
infra-orbital line of Menidia. This relation between canals and 
bones is, however, not an inflexible one, as evidenced, for 
example, by the fact that, even among the siluroids, the supra- 
orbital and infra-orbital canals may separate either in the frontal 
or in the post-frontal, and still more clearly by the presence of 
a canal and a sense organ in the inter-operculum, as well as the 
pre-operculum, of Chaetostomus (PoLLARD) and of Clairas, ac- 
cording to CoLLINGE (’95, p. 277). Moreover in cases where 
the dermal skeleton is greatly reduced, while the sensory organs 
of the lateral line system do not suffer a corresponding reduc- 
tion, as in Lophius, the canals disappear and the courses of the 
lateral lines, as indicated by the rows of naked sense organs, 
cease to be dependent upon the positions of the underlying 
bones. For instance, it appears from the careful descriptions 
and figures of Guiret (’g1) that the opercular line of Lophius 
has been displaced far backward, so that instead of lying over 
the pre-operculum, it lies over the operculum and sub-opercu- 
lum. Batrachus (Capp, 99) exhibits some interesting transi- 
tions toward the conditions found in Lophius. 
