238 PNEUMONOBRANCHIATA. 



whorl of the adult shell is often very gibbous. These 

 variations have caused the animal, when found in clear 

 quiet water, to be considered as a separate species. 



Dr. Turton's figure (Man. ed. 1. f. 102.) of Physa 

 scaturiyinum has been suspected to represent a young 

 individual of this species. It is a copy of Drapar- 

 naud's, which is a very doubtful species ; and thought 

 to be the young of some land shell. A reversed dis- 

 tortion is sometimes found. (Hanoiv Seltenheiten, ii. 

 t. l.f. 5.) 



Montagu erroneously thought that these animals 

 were unisexual ; for he observes the sexes, too, are 

 distinct, as is usual in aquatic Limaces. 



The eggs are ovate, with a yellow spot ; they are 

 united together into elongated subcylindrical or oblong 

 masses, attached to water-plants, &c. (See Pfeiffer, 

 f. 13, 14, 15.) 



Rossma'sler has described a North American 

 species, like the first variety, under the name of L. 

 speciosus (t. 2. f. 50.). 



M. Deshayes and M. Prevost have remarked, that 

 the impregnation of these animals is only accom- 

 plished by the participation of three individuals ; the 

 middle one using the functions of both sexes, the two 

 others that of the male and the female only. Some- 

 times the outer individual impregnates another indivi- 

 dual, so that the animals form a more or less long chain 

 floating on the surface of the water. 



In the Danube this species grows to four times 

 the size of the usual English variety, but does not 

 otherwise differ from it. 



