414 
OHIYOMATSU ISHIKAWA. 
rise to a very narrow tube — the proctodseum. The invagina- 
tion deepens as the embryo grows larger, and the cells lining 
its wall become columnar. The cells at the blind end of the 
proctodseum later become continuous with the peripheral cells 
of the yolk-mass (fig. 76), and thus the communication is 
made between the proctodseum and the yolk-mass. Slightly 
before the stage represented in fig. 61 a crescentic depression 
is formed between the cephalic lobes and the first pair of 
anteunse, which gives rise to the stomodseum. It is at first a 
narrow blind tube like the proctodseum, and is directed upwards 
and forwards ; but as it grows it makes a sudden turn back- 
wards, and its blind end considerably enlarges, forming a 
spacious chamber, the future cardiac division of the stomach. 
The communication between this chamber and the yolk-mass 
is opened at a much later date than that of the proctodseum, 
namely, at a stage slightly before the hatching of the embryo. 
It will thus be seen that both of these invaginations arise 
after the closure of the gastrula cavity, and independently 
of it. 
Secondary Mesoderm. — At the stage now described some 
of the yolk-segments which lie close below the embryo become 
markedly changed. They show a number of small granules 
(fig. 62, sms.), which are easily coloured by logwood solution. 
These granules are sometimes of considerable size, each having 
a clear cellular outline. They gradually come out of the mass 
and become transferred to take their position immediately 
below the ectoderm (figs. 64 and 65, sms.), mingled with other 
mesodermic cells. These are mostly aggregated in the cephalic 
region, between the involutions of the ectoderm cells, but are 
also found in all places. Their size is very small compared 
with other cells, as will be seen in the figure. The time of 
their appearance and their position seem to indicate that they 
may probably be comparable to the “ Secundare Mesodermele- 
mente” of Reichenbach ( - 4 9 , V - 5 2 ) , from which they differ, 
however, in size and in general appearance. 
Nervous System. — Although my observations on this head 
are very imperfect, some of the sections I obtained show struc- 
