COMMON FRESHWATER SHELLS. 243 



that it has been generally accepted that the narrower forms inhabit 

 streams, when less resistance is offered to the running water than 

 would be the case with the more globular forms ; hence, the latter 

 inhabit ponds where there is no motion in the water. But his 

 experience does not bear this out, some of the most elongated 

 forms in his extensive collection having been taken from ponds. 

 Certainly, some specimens which I have taken from the Wharfe at 

 Poole last summer are distinctly globular. 



The eggs of this interesting mollusc are round and colourless, 

 with a whitish opaque spot at one end, and as many as eighty eggs, 

 or even more, are to be found in one mass of the protoplasmic 

 substance in which they are enveloped. This spot is the embryo 

 of the future snail and grows day by day, and may be seen moving 

 in the egg before hatching. A single individual has been known 

 to lay as many as one thousand three hundred eggs during one 

 season. " Most of the full-grown animals," says the authority 

 previously quoted, "that deposit their eggs in early summer at 

 once die off." 



Closely related to, but not nearly so common as, Limncea 

 peregra, is L. stagnalis, one of the most graceful, and perhaps the 

 most graceful of our freshwater shells. It inhabits sluggish 

 streams throughout the country. It is a lazy species, and adheres 

 very firmly to the object to which it has attached itself Another 

 habit is that of floating on the surface of the water. This species 

 differs from the last in its choice of food, Limncea peregra i>refer- 

 ring vegetable matter, whilst L. stagnalis lives principally on 

 animal matter. 



We will now take a glance at a member of an entirely different 

 family. Viviparus viviparus is interesting because its eggs, instead 

 of being left in the water to hatch — as are those of the two pre- 

 ceding species — are kept within the shell of the parent, and when 

 these are hatched the young still remain there for two months at 

 least. They have then become capable of finding their own nutri- 

 ment. When they have reached this stage, they do not all leave 

 the parental shell together, but straggle deliberately out three or 

 four at a time at intervals of several days. The mouth of Vivi- 

 parus viviparus is protected by a horny operculum or "lid." 

 The species is said to be plentiful in the South of England. 



