258 CLA YPOLE. [Vou. XIV. 
complex structures following; it is very thin excepting in places 
where the knobs are attached, which came from the trough of 
the fold. The first crenated membrane (c.r) is the next. This is 
uniform in thickness and is shed over the whole surface, includ- 
ing the precephalic organ, which is, however, unaffected by the 
crenations. By the time the last envelope, the second crenated 
membrane, is formed (Fig. 39, c.2), the dorsal organ is under- 
going the process of degeneration already described; its cells 
are elongating, the inner edge is becoming uneven, and the 
nuclei are shrinking to more solid masses (Fig. 39, fc.o.). The 
close connection between this organ and the envelope is readily 
proved by the fact that when the membrane is removed the 
organ is usually torn away from the embryo and remains attached 
to the envelope. No suggestion as to the function of the pre- 
cephalic organ can be made; there was no evidence that it is 
particularly associated with yolk absorption; its period of great- 
est development precedes the appearance of the germ band. But 
its only obvious use begins at about this time. The ultimate 
fate of the structure is gradual absorption; it becomes smaller 
and smaller, as is seen at gc.o. in Pl. XXIII, Figs. 41-45. 
It loses its connection with the envelope, and remains recog- 
nizable as a darker red staining mass inside the embryo, with 
a tuft of fine threads outside. On the hatching of the animal 
it is no longer visible. 
From these facts it is clear that there is no structure present 
corresponding in origin and nature to the amnion and serosa of 
the other Insecta. These are distinctly cellular envelopes, and 
appear at a later time. The “dorsal organ,” so-called among 
the higher Insecta, is directly connected with these envelopes. 
Lemoine ('87) has discussed this organ among the Poduridae, 
describing its form in Anurophorus and Smynthurus; he also 
suggests its probable relations to the structures found in the 
other Insecta. The organ forms a conspicuous part of the 
embryo in both these genera; in the former it appears early in 
the development of the blastoderm, but in Smynthurus its 
appearance is delayed until the formation of the ventral plate, 
and it persists until hatching. As no sections were cut, the 
discussion of the relations existing between this organ and the 
