No. 3. ] LATERAL LINE OF AMIA. 501 
3. Sense-organs of the Spiracular Canal. 
Wright (No. 20, pp. 481 and 489) has described a patch of 
neuro-epithelium at the upper end of the spiracular canal in 
both Amia and Lepidosteus. It is supposed by him to have 
developed in this canal, and hence to be of hypodermal origin. 
In the young of Amia this sensory patch is a group of organs 
exactly like the regular organs of the lateral canals, consisting, 
as they do, of a large central organ and two or more smaller 
terminal ones. The group lies in the median wall of the mem- 
branous spiracular canal near its blind upper end. 
The spiracular canal in Amia (No. 20, p. 492) opens widely 
on the upper surface of the cartilaginous cranium, at the 
extreme anterior end of what is rather a diverticulum of the 
temporal groove of Sagemehl (No. 13, p. 188) than a part of 
the groove itself. The main groove lodges the anterior end of 
the trunk muscles, while the diverticulum, which lies wholly 
lateral to it, connected with it along its edge, lodges no muscles 
whatever. It contains only loose, fatty tissues, vessels, and 
nerves. The squamosal portion of the infra-orbital canal lies 
directly above this diverticulum, and that branch of the R. 
oticus facialts that supplies organs 15 and 16 of that line lies in 
it, running backward from the point where the nerve issues 
through the roof of the cranium median to and about on a 
level with the opening of the spiracular canal. A branch of 
this same nerve, given off just as it leaves its foramen, turns 
outward and downward into the upper end of the spiracular 
canal, and is distributed to the group of organs there in the 
same way that the nerves of the lateral canals are distributed 
to the organs they supply. 
When it is remembered in connection with the innervation 
and position of this group of organs, that all the sense-organs 
which at this stage lie inside the canals of the lateral system, 
are in earlier stages found on the external surface of the head, 
it seems reasonable to suppose that this particular group in 
Amia, apparently so anomalous in position, was regularly devel- 
oped in the epidermal covering of the head along with the other 
organs of the infra-orbital line, but, lying near the edge of the 
spiracular cleft, it wandered into this cleft as it was closed, and 
so acquired its present position. If this be so, the lining mem- 
