go THE LIFE OF THE MOLLUSCA 
100,000,000 ova. A portion, supposed to be one- 
seventh of the ovary of a Ship-worm (Teredo) was 
estimated to contain 1,874,000 eggs. For Chiton 
200,000 is quoted. Among Cuttlefish Loligo and 
Sepia are said to have 30,000 to 40,000. A single nida- 
mental ribbon of the Sea Slug (Archidoris) has been 
reckoned to enclose 50,000 to 300,000, The single 
capsules of Purpura lapillus—and one individual, it 
is said, has been observed to produce 245 of them— 
contains from 400 to 600 eggs, of which, perhaps, 
only ro to 16 attain maturity, the remainder serving 
as their food while in the capsule. The Pulmonata 
lay comparatively a small number of eggs. The 
freshwater Limpet (A ncylus) lays only 5 or 6, Limnea 
and Planorbis 20 to 100 in each mass. The common 
Garden Snail (Helix aspersa) produces 40 to 100. 
The viviparous forms average fewer, Vivipara bring- 
ing forth about 15, and the Stenogyridze about 4 or 
6. The eggs of many of the Land Snails have a 
regular calcareous shell, and are sometimes of great 
size, those of the African Achatina and the South 
American Strophocheilus (Plate XXX., Fig. 1) rivalling 
a pigeon’s egg in magnitude. 
In most cases the eggs or young are at once 
abandoned to their fate, but in some instances a 
partial protection is extended to them in their early 
stages. Occasionally the eggs are attached to the 
parent shell. This is the case in Liomesus Dalei, 
while several species of Theodoxis and Septaria have 
