No. 3.] MUSCLES AND NERVES IN AMIA CALVA. 631 
there is a line of surface organs on the outer surface of the 
opercular bones immediately behind the preoperculum. They 
are all innervated bya special branch of the mandibularis exter- 
nus facialis, and are therefore of the character of pit organs, and 
unquestionably represent in Gadus one of the cheek-lines in 
Amia, or a similar line not found in Amia. One of these 
organs has possibly become inclosed in a canal or tube in 
Chaetostomus. The organ may, however, belong to the main 
canal line, for Collinge states (No. 20, p. 277) that the 
operculo-mandibular canal in Clarias nienhofii traverses the 
inter-operculum. Pollard, unfortunately, does not describe 
the operculo-mandibular canal in Clarias. Collinge’s state- 
ment cannot therefore be controlled, and his statements seem 
sometimes to need considerable control or confirmation. 
In Esox lucius, for example, Collinge says (No. 20, p. 288), 
“there is a distinct and very large lateral canal’ extending 
the full length of the body. I find only a lymph canal lying 
under the dermis. Other investigators have doubtless only 
found this same canal, as, according to Collinge’s own state- 
ment, they find no lateral canal. In Salmo salar he describes 
(No. 20, p. 296) ‘‘a series of functionless canals passing through 
the substance of the bone”’ and not communicating with the 
surface ; and a series “‘of small, drainpipe-like ossifications ”’ 
from which have arisen a “‘more superficial series of canals,”’ 
“which gradually replaced altogether those traversing the 
deeply seated cranial elements.” In Salmo namaycush I find 
the canals traversing the same bones they do in Amia, except- 
ing only the antorbital and ethmoid. The extrascapular of 
Amia is, however, represented in Salmo namaycush by a series 
of small, tube-like bones, such as Collinge describes in Salmo 
salar, and there is a small bone of a similar character between 
the upper end of the preoperculum and the lateral edge of the 
squamosal. As the canals in Coregonus (white fish) also lie 
in the main cranial bones, Collinge’s statement regarding 
Salmo salar seems most exceptional, the process of develop- 
ment he assumes still more so. Why organs once found in 
canals resembling those of other fishes should afterwards 
migrate into a secondary, superficial series of canals, certainly 
