No. 3-] LATERAL LINE OF AMIA. 531 
which takes place in Amia, and the two pores, always found single 
in other specimens, were each represented by a group of two. 
2. Origin of the Canal Organs. 
The discussion of the origin and growth of the sensory 
thickenings from which the different lines of the lateral system 
arise, and the origin of the sense-organs along these lines, lies 
wholly beyond the scope of the present paper, but the order 
and manner of their appearance, as determined from surface 
examinations, lies fairly within it. Most of the specimens used 
in this part of the work were killed in picro-sulphuric acid or 
chromic acid, with, or without, a trace of osmic, or in the vapor 
of osmic acid, and then transferred to chromic. Chromic acid 
was found to emphasize the continuity of the whitish lines which 
represent the sensory tissues, while picro-sulphuric produced a 
somewhat opposite effect, making evident a want of continuity, 
or at least a difference in the composition of the lines in those 
places where the innervation changes. Freshly killed speci- 
mens were found to give much the best results, for the use 
of alcohol obscured the markings which in certain places are 
indistinct even in the best preparations. 
In fishes just hatched, the lines of the infra-orbital, supra-orbi- 
tal, and lateral line canals are the only ones that can be distin- 
guished. They are all represented by short, straight, raised 
lines of about the same length. That of the lateral canal _ 
starts immediately above the opercular opening, and those of the 
other two close together (if not from a common point), imme- 
diately behind the eye and directed, like the arms of a letter V, 
one above and the other below it. In somewhat older speci- 
mens the infra-orbital line extends under the eye to the level 
of the hind edge of the nasal pit, where it ends in an enlargement, 
from which later (Fig. 1, Pl. XXX.) the anterior commissure 
is given off downward and forward, the main line continuing 
upward toward the nasal pit. Behind the infra-orbital line, and 
immediately above the opercular opening, there are at this age 
two short, curved, comma-like lines directed upward and back- 
ward with their enlarged ends behind. The anterior one is the 
rudiment of organ 17 and the middle dorsal pit line, and the 
other the rudiment of the supratemporal and posterior dorsal 
pit lines. They both lie on the anterior end of a raised surface 
which is continuous with the dorsal part of the body muscles, 
