IN A SNAILERY. 15 



The pulmonates unite both sexes in one individual, but 

 it requires the mutual union of two individuals to fertilize 

 the eggs. The eggs are laid in May or June, when large 

 numbers of snails gather in sunny places. When about to 

 lay, the snail burrows into damp soil or decaying leaves, 

 underneath a log, or in some other spot sheltered from the 

 sun's rays, and there drops a cluster of thirty to fifty eggs 

 looking like homeopathic pills. Three or four such de- 

 posits are made, and abandoned. This is the ordinary 

 method of the genus helix, but some of the land and all 

 the pond-snails present variations. The ova of slugs are 

 attached by the ends in strings, like a rosary, and many de- 

 posits are made during the year. Bulimus and other South 

 American genera isolate each egg, which in the case of some 

 of the largest species is as big as a pigeon's. Vitrina and 

 suecinea glue them in masses upon stones and the stems of 

 plants, while the tropical bulirni cement the leaves of trees 

 together to form nests for their progeny. The pond-snails 

 hang little globules of transparent gelatine containing a few 

 eggs, or otherwise secure their fry to wet stones, floating 

 chips, and the leaves of aquatic plants. In neritiria, a brack- 

 ish water inhabitant, the ova, immediately upon being laid, 

 become attached to the surface of the parent's shell, and 

 when the embryo hatches each egg splits about the middle, 



