1912.] NATURAL SCIENCES OF PHILADELPHIA. 183 



budding. On the other hand, Woltereck's (1909) Daphnia were 

 parthenogenetic. These "lines" of animals therefore cannot be 

 compared strictly with those "lines" in plants that reproduce 

 through self-fertilization. 



Adhering strictly to Johannsen's definition, as far as I know no 

 experiments with pure lines have ever been performed with animals. 



Lymncea, after this superficial study, would seem to furnish such 

 material : 



1. It apparently does self -fertilize its eggs when isolated. 



2. The time for generation is short — two to three months. 



3. There are a few well-defined characters that may be observed. 



4. Hybridization is possible, but as far as Lymncea columella from 

 this region is concerned, it is rarely that more than one species is 

 found in a single habitat. There is no evidence, as yet, that it is 

 not homozygous. 



On the whole, Lymncea columella seems to combine some of the 

 necessary requirements on which to base a pure-line investigation. 



Literature. 



Adams, C. C. 1900. Variation in Io. Proc. of the Am. Ass., IL, 208. 



VON Baer. 1835. Selbstbefruchtung an einer hermaphroditischen Schneeke 



beobachtet. Midler's Arch. f. Anat. u. Phys., Jahrg. 1835, 224. 

 Baker, F. C. 1911. The Lymnceidae of North and Middle America. Chicago 



Academy of Sciences, Publication No. 3. 

 Baker, H. B. 1910. Variation in Lymncea reflexa Say from Huron Count v. 



Twelfth Report of the Mich. Acad, of Sci. 

 Bratjn. 1888. Zur Frage der Selbstbefruchtung bei Zwitterschnecken. Nach. 



d. deutsch. malakozol. Ges., XX, 146. 

 Bronn. 1889 and 1900. Klassen und Ordnung des Tierreichs. 

 Chaster. 1899. A Cross between Lymncea stagnalis and L. auricularia. 



Jour, of Conch., IX, 282. 

 Colton. 1908. Some Effects of Environment on the Growth of Lymncea 



columella Say. Proc. Acad. Nat. Sci. Phila. 

 Handel. 1907. Vererbung bei ungeschlechtlicher Fortpflanzung von Hydra 



grisea. Jenaischi Zeitschr., XLIII, 321. 

 Heynemann. 1869. Begattung zwischen Lymncea auricularia und peregra. 



Nach. d. deutsch. malakozol. Ges., I, 37. 

 von Ihring. 1876. ,An nnsere Mitglieder. Nach. d. deidsch. malakozol. Ges., 



VIII, 49. 

 Jennings and Hargitt. 1910. Characteristics of the Diverse Races of Para- 

 mecium. Jour, of Morph., XXI, 495. 

 Jennings. 1911. "Genotype" and "Pure Line." Science, December 15, 841. 

 Johannsen. 1911. The Genotype Conception of Heredity. American Natural- 

 ist, XLV, 129. 

 Mellor. 1905. Higher Mathematics for Students of Chemistry and Physics. 

 Morgan. 1904. Self-fertilization Induced by Artificial Means. Jour, of Exp. 



Zool., I, 135. 

 Pearl. 1911. Inheritance of Fecundity in the Domestic Fowl. American 



Naturalist, XLV, 321. 

 Pizon. 1893. Histoire de la Blastogenese chez les Botryllides. Ann. des Sci. 



Natur., XIV, 1-386. 

 Sekera. 1906. Ueber die Verbreitung der Selbstbefruchtung bei den Rhab- 



docoliden. Zool. Anz., XXX. 

 Woltereck. 1909. Verhandlungen deutsch. zoologischer Gesellschaft, 1909, 115. 



