DEVELOPMENT OP PERIPATUS NOViE-ZEALANDIiE. 291 
previous paper (4). In it one of the most remarkable features 
was the presence of the yolk outside the embryo, between it 
and the vitelline membrane. It might be more correct and 
intelligible to consider this as ectodermic yolk. In P. 
capensis protoplasmic strands are present, passing from the 
ectoderm to the egg-shell, especially in the region of the dorsal 
hump, and these very probably indicate that ectodermal yolk 
was present at one time in this position. In his last paper (5) 
on the development of the Cape species, Mr. Sedgwick states 
that the ectoderm is much vacuolated and contains globules 
which he believes to be yolk up to a comparatively late stage of 
development. Thus it seems probable that both species were pos- 
sessed of ectodermal yolk. In the gastrula stage in both species 
there is no sign of any trace of yolk which probably therefore 
arises later. In P. novse-zealandise this yolk is so thick that 
it completely obscures the external characters, which cannot be 
made out in surface view till the stage at which the appendages 
are forming when the ectodermal yolk is almost completely 
absorbed. As to the mode and time of origin of this ecto- 
dermal yolk in P. novse-zealandise I am not able to make 
any statement, as in the youngest egg in which it is present it 
is already well formed, and constitutes a very thick layer; and 
I do not know whether it is derived in some way from the 
central yolk, or whether it arises as a fresh formation in the 
ectoderm cells. However, the fact that in both species it is 
absent in the gastrula stage and appears later seems to point 
to its being an ancestral feature in the development. This, as 
well as many other points of interest in the development of 
this interesting species, will unfortunately have to remain un- 
explained until someone shall be fortunate enough to obtain 
embryos of the intermediate stages. 
Summary of Dates of Embryos which are figured in 
this paper and the previous one (4). 
Previous paper (4) : 
Figs. 1 — 10. — December. Figs. 11 — 20. — April. Figs. 
