No. 2.] THE ADHESIVE ORGAN OF AMIA, 489 
2. The ends of the cells of the cups next their cavities form a 
secretion (mucous?) by which the organ is rendered adhesive. 
3. In larve 18 or 20 mm. long the adhesive organ has been 
pushed beneath the surface by the thickening of the epidermis. 
Its cells subsequently become vacuolated, leucocytes appear 
among them and the organ finally wholly disappears. 
4. There is at no time any genetic connection between the 
adhesive organ and the ectoderm, or any of the epidermal 
sense organs; nor is there more than a superficial resemblance 
between it and any of the epidermal sense organs. 
5. Ihe mesoblast of the head region is formed largely by 
delamination from the entoblast, but part of it is proliferated 
from the germinal wall bordering the crescent and part from 
the “button” (pre-oral gut). 
6. A pair of head cavities is formed in the delaminated 
mesoblast and these later communicate with one another 
across the middle line. The communication lies in the saddle 
cleft at the front end of the notochord. 
7. The head cavities are not formed by evagination from 
the archenteron, but appear in situ in the mesoblast. They 
are equivalent to the premandibular head cavities of other 
vertebrates and become later connected with the third nerve. 
CONCLUSIONS. 
An adhesive organ occurs in the larve of Amia, Lepidos- 
teus and Acipenser, and in certain Amphibia. What we be- 
lieve to be a homologous structure is found in Elasmobranchs 
and in Amphioxus. We shall not discuss the Amphibian 
organ at this time. 
Amia. Dean, in his work on the larval development of this 
form (1896), says that in the four-day larva the two halves of 
the adhesive organ are crossed transversely by a row of pig- 
ment cells which “apparently demarcate the lines of the sen- 
sory tracts.’ This existence of pigment across the adhesive 
organ as well as along the sensory tract is regarded as evi- 
dence that the cups of the adhesive organ are homologous to 
