200 



LIMNiEAD^. 



Fig. 48. 



LhnncEus pereger. 



The apex of the shell is often eroded or truncated 

 (fig. 49); that is to say, as the upper part of the body- 

 is withdrawn from the tip, and the body moves 

 forwards into the larger part of the shell, it forms 

 Fia 49 ^ septum behind, and the part that 



is thus separated eventually falls off. 

 Mr. Jeffreys, not being conversant 

 with the physiology of the INIollusca, 

 gives a curious explanation of this 

 phenomenon, which is not uncommon 

 in the terrestrial and marine, as well as fresh-water 

 Mollusca. " In the absence of other nourishment, 

 they (the Limncei) will even devour each other, 

 piercing the shell near its apex, and eating away 

 the upper folds of the inhabitants. This accounts 

 (he proceeds) for the mutilated and often imperfectly 

 repaired state of the upper volutions of some speci- 

 mens." {Linn. Tra?is. x\i. 371. But see Turton*, 

 Man. ed. 1. 78. ; Gray, Phil. Trans. 1833.) 



L. palustris. 



* Dr. Turton, by mistake, appears to think that the shells 

 have "a vascular connection" Avith the animal. This is not 



