1908.J 



NATURAL SCIENCES OF PHILADELPHIA. 



445 



in diffused daylight and six in the dark. During the daytime the jar 

 in the hght had the temperature about two degrees higher than those 

 in the dark. As the snails were of slightly different sizes, all the 

 jars were placed in a row with the snails in series from the largest to 

 the smallest. Every other jar was then put in the dark. The experi- 

 ment ran 8 days. In the following table the number of egg capsules 

 laid and the total number of eggs per individual is indicated. One 

 snail died in the dark and one died in the light. Both are left out of 

 account in the table. 



It will be seen that those in the hght laid nearly twice as many eggs 

 as in the dark. 



5. Other Effects and Observations. — Snails brought into the labora- 

 tory from the ponds lay at first a great number of eggs in a single egg 

 case, and the masses laid subsequently contain fewer and fewer eggs. 

 (See Table XXIII.) Placing two individuals together does not have an 

 effect of revivifying the fertility of the snail, but has the opposite 

 effect. 



Table XXIII. 



Table showing the number of eggs in successively laid egg cases after the snail 

 is brought into a warm room from out of doors in the winter time. 



The last eggs laid by these snails are sometimes quite abnormal. 

 Sometimes the eggs are fused, sometimes there is a capsule or a num- 

 ber of small capsules without a single egg. 

 29 



