No. 2.] ANURIDA MARITIMA. 257 
_ which, after being constricted to a rather narrow neck on the 
outer surface of the blastoderm, spread out like a fan or, when 
seen in the uncut egg, like a mushroom. In order that the 
later stages of this structure may be clear, it is necessary to 
consider some changes that have taken place in the blastoderm 
in general. The protoplasm of all the ectoderm cells has been 
increasing in amount and becoming vesicular, forming a deep 
protoplasmic layer (Fig. 37, é.c.) over the surface. This pre- 
paratory stage is followed bya rearrangement of the ectodermic 
nuclei, so as to form a wavy line (Fig. 38, e.c.); the protoplasm 
also assumes this form. No cell outlines are distinguishable; 
the whole blastoderm appears a continuous sheet of protoplasm, 
containing nuclei at certain definite intervals. After a short 
time, a very thin membrane separates from the surface. This 
is formed of thin strands connecting thickened masses (Fig. 40, 
Pl. XXII, ~.). The latter are found to have come out of the 
troughs of the folds in the ectoderm, the thin strands from 
the crests. A thin layer is formed on the precephalic organ. 
Soon after, a layer of protoplasm is separated from the blasto- 
derm having a definitely crenated form (Figs. 38, 40, ¢.1, Pl. 
XXII). The last part of the process is again repeated, and 
a second crenated membrane is formed (Fig. 39, ¢.2). In the 
region of the precephalic organ, this last membrane has pecu- 
liar relations. The elongated ends of the cells spoken of 
earlier are found to’ be directly connected with the second 
crenated membrane by thickened ends, which appear as a knob 
in cross-sections (Fig. 39, &.). These envelopes are developed 
in a way closely similar to that by which the original egg mem- 
brane is formed. The superficial protoplasm is at first mark- 
edly vesicular, and, after becoming homogeneous, is separated 
as a uniform layer. When the second crenated membrane is 
nearly formed, the ectodermic nuclei return to their original 
plane and the two layers again become parallel. 
At the end of this process there are, surrounding the egg, five 
membranes. First, the egg membrane formed in the ovary but 
by the egg (Pl. XXII, Fig. 40, ¢.m.); then the vitelline mem- 
brane, a thin but distinct envelope (Pl. XXII, Fig. 40, v.). This 
is followed by 7., the material cast off preparatory to the more 
