1912.] NATURAL SCIENCES OF PHILADELPHIA. 173 



LYMNJEA COLUMELLA, AND SELF-FERTILIZATION. 

 BY HAROLD SELLERS COLTON. 



The following paper is a preliminary study of the pond snail, 

 Lymncea columella Say, with the particular view of its furnishing 

 material for the study of genetics. We should look to this form 

 because of the probability that when isolated from one another, 

 the eggs that are laid are self -fertilized. No studies have yet been 

 made on animals that reproduce by self-fertilization, so that, as 

 pointed out by Jennings, 1911 B, no work on animals can be directly 

 compared with that on plants. 



Notwithstanding the many means by which hermaphroditic 

 animals prevent self-fertilization, a number of cases are well 

 known where normally self-fertilization does occur. As an example 

 of this the following groups may be quoted: Rhabdocoel Turbel- 

 larians, Sekera 1906; Polystomum, Zeller 1876 j 1 the digenetic Trema- 

 todes, Leucart, v. Siebold, Zaddock, Voeltzkow, and others; the 

 Cestodes, Loess, Carlisle, Schultze, Bellingham, van Beneden, 

 Pagenstecher, Leuekhart, 2 and others; the Ascidians Cynthia and 

 Molgula, Morgan 1904; Botryllus, Pizon 1893; and the pond snail 

 Lymncea. 



This paper will not discuss the adaptability of the material from 

 the Flat Worms or the Ascidians for breeding experiments. Parasites 

 and marine animals furnish great difficulties at the outset for such a 

 study, and Rhabdocoels reproduce also asexually, so we will turn at 

 once and consider the case of the pond snail. 



The first point to be determined is: Does Lymncea self -fertilize 

 its eggs? Oken (1817) 3 isolated an individual adult Lymncea. After 

 an interval of some months this snail laid fertile eggs. Oken con- 

 cluded that this was a case of self-fertilization. Von Hiring (1876) 

 showed how in many gastropods, Helix, for example, a long period, 

 as much as a year, may intervene between copulation and egg-laying. 

 Because of this he did not consider Oken's experiment of any value. 



1 See Bronn, 1899 and 1900. 



2 See Bronn, 1899 and 1900. 



3 See Braun, 1888. 



