THE FERTILIZATION PROCESS IN THE SNAIL. 73 



third day for a period of about twenty-five days, rests a few days, 

 then begins another cycle of laying. This is continued through- 

 out the year. Of fifty- four L. s. apprcssa isolated from the same 

 egg mass, seven laid their first eggs fifty-eight days after hatching. 

 However, they do not reach their maximum laying capacity until 

 they are about one hundred days old. The first mass is usually 

 small, containing not more than twenty to twenty-five eggs. How- 

 ever, I have recorded instances in which the first mass contained 

 two or three times this number. Kunkel states ('08) that two L. 

 st agnails deposited twenty-eight and thirty masses, respectively, in 

 about fifteen months. Another individual deposited one hun- 

 dred and sixty-eight masses in thirteen months (Holzfuss, '14). 

 My snails were more prolific than this. An adult wild L. s. ap- 

 pressa was isolated in a two-gallon aquarium and given the best 

 attention possible, that is, the water was never permitted to be- 

 come the least stagnant, fresh leaf lettuce was always available 

 for food and a green cabbage leaf was kept in water for her to 

 oviposit on. She laid seventy masses, averaging between eighty 

 and one hundred eggs each between November eleventh and the 

 following June first. Most of these eggs were incubated until 

 the embryo developed a shell. Thus it was found that at least 95 

 per cent, of the eggs of this isolated individual were viable. 

 Similar tests were made with the eggs of a number of virgin 

 Physa sayli and L. .?. apprcssa with about the same results. Al- 

 though no actual experiments of this nature were made with 

 virgin L. cohnnclla and L. palustris eggs, casual observations in- 

 dicate that the results would be comparable to those obtained for 

 L. s. appressa and -Physa sayii. 



Planorbis trlvolvls appears to offer an exception. Four in- 

 dividuals were isolated In ovo and carefully reared in isolation 377 

 days without their laying a single egg. The four snails deposited 

 ten to fifteen small empty egg-mass cases during this time. Like- 

 wise no eggs were deposited by the control culture consisting of 

 two individuals in a fingerbowl. My experience indicates that 

 in all the pond snails studied, except Planorbis trlvolvis, " virgins," 

 i.e., individuals isolated in ovo, lay as many eggs as individuals in 

 mass cultures, and that the percentage of viability of these virgin 

 eggs is as high as that of those from snails reared in mass cul- 

 tures. 



