274 HOLMES. [Vol. XVI. 



capsules is quite small ; in fact, the sides of the capsules are 

 generally in contact, leaving only the interstices to be filled 

 by this material. The amount of albumen in the capsules, in 

 comparison with the size of the Q.g%, is, on the other hand, very 

 large. The diameter of the ^gg measures about .13 mm., while 

 the diameter of the capsule is .6 mm. The egg mass is of a 

 yellowish color in the species studied, and sufficiently transparent 

 to enable one to successfully study the living embryo in situ. 

 There is less jelly than in the Qgg masses of Physa and 

 Lymnaea, and the membrane surrounding the capsule is less 

 tough. The eggs may be readily teased out of the capsules, 

 whereas in Physa and Lymnaea the capsules come out of the 

 jelly entire, and slip around like rubber balls when the attempt 

 is made to tease them apart by needles. 



The time during which P. trivolvis lays its eggs extends from 

 early spring until the fall. The eggs are deposited in the great- 

 est abundance in the spring. Where the snails are abundant, 

 stones may frequently be found almost entirely covered by the 

 00:2: masses. Often the snails themselves have several clusters 

 of eggs attached to different parts of the shell, and sometimes 

 the &gg masses may be found adhering to the bodies of aquatic 

 insects. When kept in an aquarium, the snails, in the early 

 part of their laying season, readily deposit their eggs on the 

 glass ; but later in the year, when the eggs are produced in less 

 abundance, the animals become apparently more particular as 

 to where they lay, and seldom deposit their eggs unless upon 

 stones or aquatic plants, upon which they find minute algae, 

 which serve for food. 



Usually a capsule contains but one Q.gg, but sometimes it 

 may have two, and rarely three or more. When there are more 

 than one egg in a capsule, often only one of them develops 

 normally, yet two embryos in a late stage of development may 

 sometimes be found in the same capsule. It is common to 

 find some of the eggs in a cluster developing abnormally, and 

 the proportion of such eggs is increased when the water 

 becomes contaminated. If eggs are obtained from snails kept 

 in an aquarium, care has therefore to be taken that the water 

 is kept fresh and pure. With proper feeding and attention. 



