178 
oblique muscles and the ventral body wall. In ripe 
specimens there is often also a considerable mass of 
genital products behind the third diaphragm, and pushing 
it forwards into a pouch-like outgrowth (or two such out- 
growths, one at each side of the alimentary canal). This 
is due to the fact that while the perforations in the 
diaphragm allow the passage forwards of the waves of 
eelomic fluid (see above), they do not permit the passage 
of the ova, or spermatid masses, to any extent. These 
are, therefore, as it were filtered out of the ecelomie fluid, 
and collect in a more or less compact mass behind the 
ventral portion of the diaphragm. 
The genital products escape from the animal by 
means of the last five pairs of nephridia, the terminal 
vesicles of some of which are often found to be distended 
with ova or spermatozoa during the breeding season 
(fig. 26). In a specimen 200 mm. long the vesicles of 
some of the nephridia were 14 mm. long and 6 mm. in 
width owing to distension by ova, while in another speci- 
men the vesicles were filled with sperms, and were 5 mm. 
in length and 4 mm. broad. The funnel of the nephri- 
dium is usually widely open during the breeding season. 
During the discharge of ova from the female the eggs are 
caught m considerable numbers by the slimy mucus which 
covers the body. Nothing further is known, however, 
about the oviposition. tipe females, with the caelom 
filled with ova, are found during the later portion of 
February and during March, but by the end of the first 
or second week in April the ova are usually all discharged. 
Nervous System. 
The central nervous system is composed of the brain, 
the cesophageal connectives, the stomato-gastriec system 
and the ventral nerve cord. 
