SELF FERTILIZATION IN THE AIR-BREATHING POND 



SNAILS. 



HAROLD SELLERS COLTON, 

 UNIVERSITY OF PENNSYLVANIA. 



The author has already shown that under certain conditions 

 self fertilization is possible in the common pond snail Lymntza 

 columella Say. 1 In this paper he wishes to point out that it is 

 common in species representing most of the important genera of 

 the order Basommatophora, the order which includes the air- 

 breathing pond snails. 



The criteria on which self fertilization in Lymncea columella 

 has been determined is as follows: (i) The snails are hermaphro- 

 ditic and eggs and sperm are ripe in the ovotestis at the same 

 time, (2) self fertilization is mechanically possible and self copula- 

 tion has been observed, (3) two polar bodies are found on the 

 eggs produced by snails isolated from their fellows from the 

 time of hatching, (4) normal parthenogenesis is unknown in the 

 Mollusca. The chances therefore that the phenomena observed 

 is parthenogenesis and not self fertilization is very nearly nil. 



In every case the following method was used. A snail was 

 isolated and placed in a jar holding from 300 to 500 c.c. of filtered 

 pond water. A pinch of dry garden soil was added 2 together 

 with a dry leaf or two from a Carolina poplar tree for food. 

 When the snail laid eggs and these hatched, each young one, when 

 a day or two old, was isolated and placed in a jar under the con- 

 ditions stated above. If these young snails grew to adult size and 

 laid eggs which in their turn developed, then self fertilization was 

 assumed. 



The material used was Lymncea columella from around Phila- 

 delphia, Lymncza columella from Chicago, Lymn&a humilis 

 modicella Say, from Philadelphia ponds, Lymncea catascopium 

 Say, from the Delaware River near Torresdale, Pa., Lymntza 



1 Colton, Proc. Acad. Nat. Sci. Phila., May, 1902. 



2 Colton, Proc. Acad. Nat. Sci. Phila., July, 1908. 



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