502 ALLIS. [VoL. Il. 
brane at the upper end of the spiracular canal must be ectodermal 
rather than entodermal in origin. No positive evidence of this 
method of development has yet been found, for in none of the 
postembryonic forms to which the present work has so far been 
confined has the spiracle been open. In some of the youngest 
specimens, however, certain appearances seemed to indicate that 
it had only recently been closed. In specimens from one to five 
days old there is always a strong depression immediately above 
the upper end of the opercular line (Figs. 1 and 3, Pl. XXX,, 
spr). The developing infra-orbital line crosses this depression, 
and organs 15 and 16 lie in it. In freshly prepared one-day- 
old specimens there is in the bottom of the depression, imme- 
diately below these organs, a dark spot indicating the position 
of the blind upper end of the spiracular canal. This spot in 
some specimens is strongly marked, and if the tissues are fresh 
and somewhat transparent, has the appearance of being an 
opening with a part of the sensory tissue of the infra-orbital 
line extending into it or across its edge. 
4. Lines of Pit Organs. 
There are in Amia, in addition to the sense-organs found in 
the lateral and spiracular canals, several surface lines of some- 
what similar organs, which, although belonging to the same 
general class of nerve-hillocks (Merkel), differ greatly from the 
canal organs in shape, arrangement, and method of multiplica- 
tion. These organs are somewhat conical in shape, and, like 
the canal organs, represent the entire thickness of the epidermis 
at the points where they occur. In young fishes, and on the 
body in the adult, they project slightly beyond, or come nearly 
to the level of, the outer surface; but on the head of the 
adult they lie at the bottom of little pits, and therefore they 
may be called pit organs. They are found close together, in 
regular lines on slight dermal papillz, and are connected by a 
special cord of cells which extends beyond the end of the line, 
and is lost among the general epidermal cells. They appear to 
develop independently along this cord. 
Cut 5 represents a section through one of these surface lines 
in an adult; and Cut 4, one in a fish 45 millimetres long. Cuts 
4 to 9 are semi-diagrammatic, but the outlines are taken from 
