434 
respects from TRAQuAIR’s. POLLARD (No. 11), in 1892, and before the 
publication of CoLLınse’s paper, had also investigated, to a certain 
extent, the lateral system of Polypterus, but he did not describe the 
full course of the canals, and the only drawing that he gives, that 
shows them, is a wood-cut said to be taken “chiefly from WIEDERS- 
HEIM”. Whether WIEDERSHEIM made any investigation of these canals 
himself, or not, I do not know, not being able to consult his “Lehrbuch”, 
to which alone of this author’s works POLLARD makes reference. The 
canals in PoOLLARD’s figure differ somewhat from those given by either 
TRAQUAIR Or COLLINGE. 
The slight, but nevertheless morphologically important, differences 
in these several descriptions, certain features in COLLINGE’s descriptions 
that seemed to me wholly improbable, and above all the wish to know 
whether the supratemporal commissure of Polypterus was the homo- 
logue of the one in Amia, or the homologue of such a commissure as 
SAGEMEHL has described (No. 13, p. 37) in the Characinidae, have led 
me to carefully investigate the canals myself. In this work I have 
not attempted to do more than simply control, in a general way, PoL- 
LARD’s descriptions of the innervation of the canals; that is, I have 
found the ends of the nerves that innervate each of the sense organs 
enclosed in the canals, and have taken sufficient account of their 
general superficial position to be able to affirm that they all probably 
have the internal origin ascribed to them by PoLLARD. I may, however, 
as well here state that the little work I have so far done on this fish, 
has decided me to undertake a careful investigation of its skull, and 
also of the cranial portions of its nervous and muscular systems. 
For the examination of the lateral canals I have used. a 44-cm 
and a 30-cm specimen. The descriptions, however, relate entirely to 
the 44-cm one unless otherwise stated, and the accompanying figures 
1 and 2 are of that fish. 
In alcoholic specimens considerable portions of the external sur- 
face of the head of Polypterus are bare, that is to say the dermal 
bones of these regions are covered only by a thin layer of dermis. 
The end and top of the snout, and the portions surrounding the eyes 
and nasal apertures and bordering the mouth are, on the contrary, 
covered by a tough, and in certain places thick dermal tissue that 
completely covers and conceals the underlying bones. Posteriorly a 
narrow band of this tissue edges the dorsal and ventral edges of the 
series of prespiracular, spiracular, and postspiracular ossicles, while 
a large band of it extends backward from the hind end of the mouth 
to the ventral end of the opercular bones, and then extends upward 
