230 SNAILS AND SLUGS [CH. VII 



It may be mentioned that in the Limnceidce the male and 

 female apertures are separate from one another, the latter 

 being situated beneath the mantle flap some distance from 

 the former which is placed as in Helix. The details of 

 oviposition are better known in Arion ater than in Helix 

 pomatia. Two individuals are recorded to have deposited 

 respectively 396 and 477 eggs in the course of one autumn. 

 Individual A deposited 80 eggs on October 10th, 110 on 

 16th, 77 on 25th, 82 on November 8th and 47 on 17th: 

 B deposited 246 on October 13th and 14th, 9 on 26th, 121 

 on November 10th and 101 on 30th. The young hatched 

 in from forty to seventy-four days, those of any one batch 

 not hatching simultaneously. The young slugs were about 

 9 mm. long at birth; in five months they were 56 mm. 

 long and were full grown in about a year and a half. Death 

 occurred at about 2 years of age. In the case of Helix 

 aspersa also details of the life-history have been published. 

 The eggs hatched in August, about a month after being 

 deposited; before the winter the shells had attained a 

 diameter of f inch ; by October of the following year the 

 shells were 1 inch in diameter, but had no " lip " ; in July 

 of the next year a " lip " was formed, the diameter being 

 now 1^ inch (age, nearly 2 years). Mating took place in 

 August of the year following (age, 3 years) and eggs were 

 laid. The full term of life was about 5 years. The shell 

 of an old snail can be distinguished by the smooth rolled 

 back margin of the " lip." The length of life of the water 

 snails Limncea and Paludina is stated to be 3 to 4 years 

 and 8 to 10 years respectively. 



Enemies and Parasites. The enemies of our terrestrial 



