504 ALLIS. [ VoL. Id: 
stage of its development has the appearance of a flat dome 
with a large, vesicle-like space, set like a keystone at the 
top of the structure. Toward this space the cells of the organ 
are directed, and as they increase in length, and the organ in 
height, the latter pushes its way, wedge-like, through epidermal 
cells, crowding them to either side, until it reaches the outer 
surface, where its upper central portion becomes exposed. It 
has now the shape of a cone with rounded summit (Cut 4); and 
its exposed upper end, which contains the compressed outer 
ends of all the sensory cells, reaches to the general level of the 
outer surface, or even projects beyond it. On the body, and 
particularly toward the tail, the organs retain nearly this con- 
dition even in the adult; but on the head they are later so much 
withdrawn from the surface that only a series of minute holes 
indicates their position (Cut 5). 
Cut 6 is a section through the suborbital line in a fish 113 
millimetres long. It shows one of the canal organs in a stage 
corresponding to that of the young pit organ in Cut 4, and also 
to that of the organs of the lateral line in Salmon embryos 
before the organs have reached the outer surface, as shown by 
Hoffman (No. 8, Pl. V., Fig. 29). There is at the top-of this 
canal organ the same vacuolar space that is found in the develop- 
ing pit organ, and there are apparently no support cells. These 
appear later, after the organ has reached the outer surface, as 
shown in Cut 7. 
In these early stages the different organs of a canal line are 
connected by a special cord of cells similar to that connecting 
the organs of a pit line. In Cut 8 the organ has begun to sink 
below the surface, and in Cut 9 the canal is just closing over it. 
As development progresses, the connecting cord of cells disap- 
pears, except immediately adjoining the organ, where it was 
present in the oldest specimen in which it was examined, one 
about 80 millimetres long. Along this remnant of the cord, 
and immediately adjoining the primary organ, the other organs 
of the group appear, at first as small bud-like organs, inclined 
away from the larger central one (Fig. 48, Pl. XLI). These 
new organs grow rapidly, and others soon appear in succession 
along the cord beyond them, all at first in contact at their bases, 
but separated above by projecting ridges of indifferent cells, ex- 
actly as figured and described by Blaue (No. 2), in the olfactory 
