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Notes on the Life - History of Planorbis 



corneus and Other Freshwater Mollusks 



WILLIAM T. WEBSTER, F. R. M. 5. 



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At the previous meeting of this society 

 I had the pleasure of bringing to your 

 notice the occurrence of a red form of 

 Planorbis corneus, and in stating the fact 

 that many freshwater snails cannot live 

 in association with the Cypridae. At the 

 time I made this communication, I did 

 not quite know the extent and scope of 

 this society, and my remarks were con- 

 fined to a few bare facts. I hope, to- 

 night, to go into the matter more fully ; 

 but there are still several matters in- 

 definite which I hope to clear up at some 

 future date. 



I do not make any pretensions to being 

 considered an authority on the subject 

 of freshwater snails ; my interest is en- 

 tirely centred in their utility as food for 

 fishes. In this respect the subject is one 

 of very considerable importance, and 

 possibly this red form has a far greater 

 value than any other, that is, if it be left 

 to the judgment of fishes, and if after a 

 trial, it may be found to improve the 

 flavor of fishes as food for man. I am 

 pleased to say that in fish culture circles, 

 and in other directions, considerable in- 

 terest is being taken respecting this snail. 

 I have distributed quantities over a wide 

 area, and there is probably little danger 

 now of its becoming extinct. 



In the early summer I had the pleasure 

 of conducting one of your fellows to the 

 pond where it was found, and you will 

 be interested to know that we were able 

 to find abundant evidence that the red 

 colony was an old established one, and 

 the snail had even acquired a local name. 

 With further material for study, many 

 interesting features have been brought 



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to light. Several specimens have been 

 found with nearly white bodies and nor- 

 mal shells, and some have been discov- 

 ered with red bodies and white or nearly 

 white shells. Most specimens over one 

 year old are completely perforated in 

 the centre. In many cases the hole 

 quite small, whilst in others the perfora 

 tion is large, and only the outer, or body, 

 whorl remained. In the early summer 

 all these perforations were neatly sealed 

 —quite as perfectly as if done in a turn- 

 ing lathe, and there was nothing to indi- 

 cate that they had ever possessed an 

 apex. Later in the season, the sealing 

 becam.- ragged as further erosion took 

 place. It is interesting to record that 

 nearly every specimen with a large hole, 

 if lifted carefully by hand, had a young 

 Sphaermm corneum attached to the 

 ce ntre — the bivalve dropped away when 

 a scoop was used for collecting. 



On carefully examining the tentacles 

 many peculiarities are observed. Some 

 have both extremely long, slender and 

 well matched. Some have one long and 

 one short ; the shorter is left or right in- 

 discriminately. Some have two very 

 short tentacles, stunted and conical. A 

 few were found doing well, entirely 

 without, and the places where they 

 should have been were indicated by the 

 merest suggestion. Some specimens have 

 the left tentacles bifurcated, and these 

 having been isolated and mated, all the 

 young proved normal. None has been 

 found with a single tentacle. 



The mating of the red form with the 

 normal always produces dark offspring, 

 and if two of these dark ones are mated. 



