4&8 REIGHARD—PHELPS. [Vou. XIX. 
branches, which open one into each of the four median cups. 
The thickened epidermis is filled with pigment. Numerous 
sense buds also occur in it and through it the lateral line 
canals open to the exterior. 
When the larva reaches 20 mm. in length (Fig. H), the 
median opening of the adhesive organ has disappeared and 
there is no external sign of the organ; but in sections (Fig. 
H1) it is found to exist as a pair of irregular ovoid masses, 
one mass lying on either side of the median plane beneath the 
much thickened epidermis. The central portion of each of 
these is made up of an extremely vacuolated central mass, the 
remains of the central portions of the cells of the former 
cups. A few leucocytes occur among the meshes of the spongy 
core, surrounding which is a relatively thin sheet or layer 
which takes the stain heavily. It is evidently made up of the 
remnants of the peripheral ends of the cells of the former 
cups and contains the nuclei and all that is left of the proto- 
plasm of these cells. The whole structure bears histologically 
a strong resemblance to the notochord in certain of its stages. 
This outer, deeply stained covering is wanting on the ante- 
rior faces of the ovoid masses where a median neck of ecto- 
derm connects the two masses with the epidermis. This neck 
of ectoderm marks the position of the tunnel which led from 
the adhesive organ to the exterior in the 18 mm. larva. As 
the epidermis has thickened the tunnel has become entirely 
closed. A few days later no trace of the adhesive organ is to 
be found. 
SUMMARY OF OBSERVATIONS. 
1. The adhesive organ of Amia is an entoblastic structure 
which is developed from an unpaired fundament as a pair of 
curved cylindrical diverticula of the foregut. Each diver- 
ticulum subsequently loses its connection with the foregut 
and breaks up into six to ten closed vesicles. Each vesicle 
then acquires an opening at the surface and becomes thus con- 
verted into a cup continuous with the ectoblast. 
