ANODONTA., 269 
Hence we have— Ovotestis 
genital duct 
albumen gland 
common duct 
) | |, Q 
oviduct 
vas deferens 
spermatheca and duct 
flagellum 
| mucus glands 
penis 
vagina 
dart-sac 
The functions of these organs, so far as known, are :— 
The snail is a frotandric hermaphrodite, z.e., the male organs 
become mature first and the female after. The ovotestis gives rise to 
spermatozoa, which pass down the genital duct, the common duct and 
the vas deferens into the flagellum. Here they are aggregated into a 
rod-like mass, the spermophore. During this process darts are.secreted 
in the dart-sac and forcibly ejected from the genital pore into the skin of 
other snails. This is followed by copulation, when the sperms are intro- 
duced by the penis of one snail into the base of the spermathecal duct 
of another. They pass up into the spermatheca and are there retained. 
The ovotestis next produces eggs which pass down the genital duct 
to the head of the common duct. The sperms then leave the sperma- 
theca, make their way down the spermathecal duct and back again up 
the oviduct and common duct, at the upper end of which they fertilise 
the eggs. Albumen is then added to the eggs from the albumen gland, 
and they pass down to the vagzza. Here they are covered with mucus 
from the mucus glands and are discharged to the exterior. In some 
species they are contained in calcareous shells. The eggs are laid in 
damp earth and the development is embryonic, the young newly-hatched 
snail differing little from its parent. 
II.—ANODONTA. 
PHYLUM MOoLLusca (p. 282)., 
Cass LAMELLIBRANCHIATA (p. 284). 
Anodonta cygnea* (the freshwater mussel) is a con- 
venient example of the large and important class 
of Lamellibranchiata, or bivalve molluscs. A 
full-grown individual may be as long as five inches. The 
Habits. 
* This description also applies to Anodonta anatina. 
