No. 2.] THE ADHESIVE ORGAN OF AMIA. 491 
subsequently considered its constituent papillz as “thickenings 
of the epiblast” and says: “These papilla are probably sensi- 
tive structures, but I have not yet investigated their histo- 
logical characters.” Balfour and Parker (1882) subsequently 
considered the organ as composed of mucous cells, which were 
highly modified cells of the mucous layer of the epidermis. 
These cells they believed to pour out a sticky secretion. In- 
vestigations now in progress in this laboratory, which it is 
hoped shortly to publish, have shown that the adhesive organ 
of Lepidosteus has essentially the same developmental history 
as that of Amia. There is as little ground for considering 
its papilla to be either ectoblastic or sensory as in the case 
of Amia. 
Acipenser. Von Kupffer (1891) describes an organ which 
he calls the adhesive organ. It arises as-a cushion-like thick- 
ening of the nervous layer of the ectoblast immediately dorsal 
to the stomodeum. The organ, as figured externally (v. 
Kupffer, 1891, Pl. 1), has somewhat the form of a crescent 
with enlarged ends which point dorsally. The convexity of 
‘the crescent lies just above the roof of the mouth. Three 
days after hatching the adhesive organ separates into two 
parts which have the form of hemispherical protuberances 
separated by the cleft-like space between the medial ends of 
the superior maxillary processes. Later each of the two parts 
of the adhesive organ thus formed again divides into two, 
so that there are four spherical projections which lie in a 
slightly curved row above the upper jaw. These become the 
four barbels of the adult. 
In view of what we now know of the adhesive organ of 
Amua that of Acipenser should be re-investigated, especially 
since v. Kupffer did not pay especial attention to it. He points 
out that, although the external ectoderm and the ectoderm of 
the brain are free from yolk, yet the cells of the hypophysis 
and adhesive organ are filled with the same yolk materials as 
those of the entoderm, thus making it impossible to distin- 
guish the tissues of these organs from the entoderm by means 
of stains. This presence of yolk indicates an entodermal 
