LIGIA. 93 
sheath. The anterior end of this is flagellate, and by 
contractions of the slightly muscular walls of the testis it 
is forced into the vas deferens. Here the sperm colonies 
are found bound together in masses (Pl. IV., fig. 5). The 
substance which causes this cohesion is probably secreted 
by a number of large cells which are situated in the 
anterior end of the vas deferens near the openings of the 
testes. 
In the female the ovaries are very conspicuous in the 
breeding season, entirely filling up the dorsal part of the 
body cavity. They he at each side of, and beneath, the 
heart, and extend from the first thoracic segment to about 
the fourth abdominal segment. They are usually filled 
with eggs of approximately the same size. A_ short 
distance behind the middle of the ovary a thin walled 
oviduct is given off. This opens to the exterior by a small 
longitudinal slit at the base of the fifth pair of pereiopods, 
immediately at the base of the brood pouch lamellae, these 
being the last pair of brood pouch lamellae. 
The ova are large, oval in shape, and contain a large 
amount of yolk. In copulating, the male walks on to the 
back of the female and grasps the anterior thoracic 
segments with the first three pairs of pereiopods; 
copulation may last one or more days. After the eggs 
are extruded, they are carried about by the female in the 
brood pouch, where they develop; the young remain for 
a short time in the brood pouch. 
DEVELOPMENT. 
The development of Ligza oceanica has been studied by 
Nusbaum. According to Nusbaum, the early cleavage 
is discoidal, although McMurrich has found superficial 
or centrolecithal segmentation in the Isopods which he 
has investigated. The first cleavage cell becomes separated 
