No. 2.] THE ADHESIVE ORGAN OF AMIA. 479 
interrupted dorsally and ventrally. Its form is therefore 
similar to that seen in the embryo at the time of hatching 
(Plate, Fig. 4), but its surface is not yet marked by the 
pits characteristic of the hatching stage. The median button- 
like protuberance is no longer visible. 
In section the paired diverticula are seen to open wide as 
before into the foregut. They are longer and more sharply 
curved than in the preceding stage. We may distinguish for 
each diverticulum two surfaces, an anterior and a posterior 
and two borders, a conxev outer and a concave inner (Plate, 
ies .3)2) Vhe-planes.-of the long -curved “axes ol the 
diverticula, which before intersected, have rotated so as to 
make them coincident with each other. This common plane 
meets the frontal plane of the embryo at an obtuse angle; 
that is the dorsal ends of the diverticula are posterior to the 
ventral ends. The changed relations of the planes have re- 
sulted, apparently, in carrying the dorsal ends of the diver- 
ticula forward so that they no longer touch the forebrain. 
This rotation has also changed their relation to the ecto- 
derm. In the preceding stage the convex border of each 
diverticulum was directed nearly forward and the diver- 
ticulum was in contact with the ectoderm over the middle 
portion of this border, so that there was produced a rounded 
protuberance of the external surface. In the present stage, 
owing to the rotation of the diverticula, the convexity ot each 
is directed laterally, while the anterior surface, which before 
faced the median plane, is directed forward and pushes up 
the ectoderm with which it is in contact. There is thus pro- 
duced, on each side, one of the low, rounded, U-sliaped 
ridges referred to as visible externally (Plate, Fig. 3). 
The nasal plates appear in sections of this stage. They are 
mere thickenings of the ectoderm which in Amia consists of 
an outer layer of flat cells and an inner layer of cubical cells. 
Only the inner, nervous layer is concerned in the formation 
of the nasal plates which lie near the median line just above 
the adhesive organ and in close contact with it. It is often 
hard to determine in longitudinal section the line of demarca- 
tion between the two structures. 
