No: 25] THE ADHESIVE ORGAN OF AMIA. 485 
primitive entoblast of the head region. They are formed 
therefore in situ. We have traced their origin step by step 
and have found no evidence of their being produced by 
evagination from the entoblast as described by v. Kupffer 
(1893) in Acipenser. We consider such a method of origin 
impossible for Amia. No trace of a second head cavity has 
been found. 
Il. THE RETROGRESSIVE PHASE. 
In larve 15 mm. long the adhesive organ as seen from the 
surface is in the condition figured by Allis (1889), Fig. 11. 
Its ring-shaped form still persists but it is not sharply outlined. 
It is much reduced in actual size and lies close above the 
mouth opening in the middle line, with the nasal openings on 
either side of it and slightly above it. The outlines of the 
individual cups composing the organ are still visible. The 
lateral line canals show distinctly. 
Sections of such larve and of slightly younger ones show 
the epidermis over the end of the snout to be much thickened 
and filled with pigment cells and sensory buds. Beneath it 
are the regularly arranged lateral line organs. The cups of 
the adhesive organ are found to be still connected with the 
exterior, but the great thickening of the ectoderm has con- 
verted their openings into deep narrow tubes. The cells 
which make up the walls of the vesicles have the appearance of 
being greatly elongated. Their central ends are still filled 
with mucus, but the protoplasm of their peripheral ends con- 
tains a few vacuoles. 
In larve varying in length from seventeen to eighteen milli- 
meters the only external evidence of the adhesive organ is a 
small median opening lying at the apex of the upper jaw (Fig. 
G). This opening is at first slit-like and parallel to the edge 
of the jaw, later it becomes circular and resembles closely: the 
opening of a lateral line organ. By means of sections one 
finds that the much thickened ectoderm entirely covers the 
adhesive organ except at this opening (Fig. G). The semi- 
circular halves of the organ have the appearance, as seen in 
