DEVELOPMENT OF THE CAPE SPECIES OF PERIPATUS. 195 
mass of endoderm. The whole embryo at this stage (PI. 
XIV, figs. 24 a—d) is vacuolated, the ectoderm as well as the 
endoderm, but the vacuoles of the endoderm are the largest. 
There is generally a special layer of vacuoles beneath the ecto- 
dermal nuclei, between which strands of protoplasm pass from 
the ectodermal to the endodermal reticulum. 
The blastopore is a slightly elongated structure (Part 1, 
figs, 19, 21), and is itself traversed by a loose protoplasmic 
reticulum (Pl. XIV, fig. 24 6). The endodermal layer lining 
the gut sends out a few processes into the gut which anas- 
tomose with the blastopore reticulum. The gut of young 
gastrule contains a largely developed reticulum (Pl. XIV, 
fig. 23), the remains of the previous stage. In older gastrulz 
there may sometimes be seen apparently isolated masses of 
protoplasm (Pl. XIV, fig. 24 a), which, however, are probably 
connected with the endodermal lining and eventually drawn 
into the latter. 
Just in front of the blastopore there is a large number of 
nuclei in the middle ventral line (Pl. XIV, fig. 24 a). 
Behind the blastopore there is a special area of ectoderm in 
the middle line which I have called the polar area, and which 
possesses the following characteristics: Close behind (PI. 
XIV, fig. 24 c) the surface is flat and, if anything, marked 
by a slight groove, the nuclei are more columnar than else- 
where, and there is a larger quantity of protoplasm outside the 
nuclei than in most other parts of the ectoderm. Further 
back (Pl. XIV, fig. 24 d) there is in the middle line a fairly 
large area of protoplasm containing one or more large round 
nuclei. 
The polar area extends from the blastopore backwards for 
a distance in this embryo (figured in Part 1, fig. 21) of about 
‘07 mm. The nuclei in this area will give rise to the nuclei of 
the primitive streak. 
The protoplasm of the polar area is vacuolated in the ordi- 
nary way. Fig. 21, Pl. XIII, represents a drawing under 
a higher magnifymg power of the hinder part of the polar 
area of this stage. 
