334 
CRESSWELL SHEARER. 
tion and arrangement of the segments being quite different 
from that in the full-grown condition, which is only attained 
after a considerable period. The eggs may be clearly 
examined within the capsule as segmentation and develop- 
ment proceed. The development is direct, and as the time 
for hatching approaches the young larval females are seen to 
spin round within the capsule. This denotes that they are 
about to hatch and leave the capsule and commence their 
free existence. If the capsule is placed under the low power 
of the microscope at this stage and carefully observed, it will 
be seen, as I have already said, that the little males are 
actively copulating with the small females. Every female as 
she passes out of the capsule is seen to carry a small mass of 
sperm, collected under the gut at the junction of stomach 
and intestine at the point where the ovary will subsequently 
appear (figs. 4 and 25). 
Examination of immature free-swimming females always 
shows them to be fertilised (figs. 5 and 6). If they are care- 
fully fixed and sections cut from them at this stage, it will be 
seen that the female germ-cells are not differentiated, and 
although a mass of sperm is collected at the point where the 
ova will subsequently appear, no trace of the ova can be 
detected (fig. 25). They only appear at a later date, when the 
female has grown considerably in size. They are then seen as 
a few small refractive cells when examined in the living state, 
and as small nuclei surrounded with hardly any cytoplasm 
in the stained condition lying beneath the gut and amongst 
the mass of sperm (fig. 20). Shortly after they appear it is 
seen that each one is joined by a spermatozoon, the head of 
which has become embedded or attached to its nuclear wall, 
so that ultimately the nucleus of each primitive ovum is seen 
to be composed of one part derived from the spermatozoon 
and the other part derived from the egg (figs. 20 and 24). 
These two elements of the nucleus never fuse, but retain 
their individuality throughout all subsequent oogonial growth 
(fig. 29). The double nucleus divides amitotically, each half 
separately (figs. 16-19). In the majority of the divisions the 
