464 ALLIS. (Vou. II. 
development and distribution of the cranial nerves, or the his- 
tology and function of the sense-organs. 
With a few exceptions, all these descriptions, so far as they 
relate to the cranial part of the lateral system, are of a general 
character only, giving little more than the course of the main 
canals. The development of the canals, the number and posi- 
tion of the organs, and their innervation, receive but scant 
attention. This has doubtless been largely due, as Merkel sug- 
gests, to the difficulties attending this part of the investigation 
before the introduction and perfection of modern methods of 
research ; but this cannot have been the only reason, for most 
of the work could easily have been done by any of the earlier 
writers. The purely descriptive part of the subject seems 
simply to have been neglected in the greater interest attaching 
to the histological and physiological sides, so that it is only 
within the last five or six years that the constant relations of 
the cranial canals to the dermal bones of the head, and their 
importance in determining these bones in doubtful cases, have 
been recognized. Both Sagemehl and Van Wijhe have called 
special attention to this, and Sagemehl further says (No. 12, 
p. 182, note) that the lateral canals seem to deserve a more 
careful study than has hitherto been given them. 
In Amia calva the cranial canals have been oftener and more 
fully described than in any other form. Franque (No. 6), in 1847, 
in a dorsal view of the dermal bones of the head, shows some of 
the surface openings of these canals, but in the text he does not 
refer to them, these four words only being found, “ Linea lateralis 
fere recta” (No. 14, p. 368). Bridge (No. 4, p. 620), thirty years 
afterward, in describing the skull, gave the course and position 
of the main canals, the connections they form with one another, 
and the bones they traverse, and the arrangement given by 
him agrees closely with that more fully detailed in the present 
paper. His work was mainly confirmed in 1882 by Van Wijhe 
(No. 17, p. 288), and in 1883 and 1884 by Sagemehl (No. 12, p. 
183, and No. 13, p. 36); still later by Shufeldt (No. 15), in con- 
nection with his translation of Sagemehl’s paper; and finally 
Wright (No. 18) has called attention to the sensory tissue lying 
in the upper end of the spiracular canal, and belonging, by its 
innervation, to the general lateral canal system, though classed 
by him as hypodermal and exceptional. 
