Fig. 9. — var. ovata. 



LIMN^A PEREGRA. 155 



Z. peregra only as a biological 

 variety of Limncea ovata, pro- 

 duced by living in hard running 

 water, and mentions cases in 

 which eggs of ovata were trans- 

 ferred into springs or rivulets, 

 and the animals hatched from 

 them were L. peregra, and also 

 vice versa. This, if correct, is, 

 of course, very interesting. It certainly does not agree with my 

 own out-of-door experience, some of the most elongated forms in 

 my collection having been obtained from ponds. 



Warm water produces thin shells, as vz^.thermalis ; absence of 

 lime a decollated shell ; an interesting account of which, by Mr. 

 Crowther, will be found in the Naturalist for 1879. Brackish 

 water is said to be productive of stunted L. peregra, but of this I 

 am very doubtful. There have as yet been no experiments made 

 of which I have seen any record with L. peregra of such com- 

 pleteness and so full of interest as those made with L stagnalis 

 by Carl Semper, and until this has been done there will be many 

 random guesses as to the cause of variation in this species. 



For a long period three or four varieties were all that were 

 recognised by British authors ; then Dr. Jeffreys' work extended 

 them to eleven, but since Darwin's work on the Origin of Species 

 was written, the impetus given to specialisation has been so great 

 that most small points which were then overlooked are now noted, 

 so that a great many more named varieties will be required. But 

 this extension should be made with great caution, otherwise the 

 differences will be so slight that even the authors themselves will 

 have no little difficulty in recognising their own work. 



Then, last, we have to consider the abnormal shells, some of 

 which are most strange in shape, some, no doubt, produced by 

 injuries to the mantle, some sinistrally formed, some swollen out 

 in part of their growth when food has no doubt been in abund- 

 ance, then narrowing down again when harder times have come 

 upon them ; others are scalariform, perhaps caused by some 

 obstruction to the shell-producing mantle continuing its work on 

 the same plane of convolution. Many of the abnormal forms are 



