46 THE CHICAGO ACADEMY OF S< [ENCES. 



To what extent the penis is everted, could not be satisfactorily 

 ascertained, but it is believed to be partly protruded. The penis-sac 

 probably performs very largely the sexual functions during copula- 

 tion, the penis being, in fact, but an enlargement of the vas deferens. 

 The length of time of the coitus was not determined ; Lymnaeas were 

 noted in coitu for more than a day, and it is possible that it may oc- 

 cupy several days. 



Crosses between different species of Lymnseas have been ob- 

 served. Heynemann 1 records a cross between Radix auricularia and 

 Lymncea percgra, the former acting the part of the female and the 

 latter that of male. Chaster 2 records a cross between Lymncra stag- 

 nalis and Radix auricularia, the former performing the function of 

 the male. The specimens were taken in copulation by Mr. H. E. 

 Craven at Litchfield, England. The union was not observed to be reci- 

 procal. The progeny were good examples of percgra and the query 

 is raised (by Chaster) as to whether percgra may not be the ancestral 

 form of stagnalis and auricularia. Recently the writer has observed 

 Lymncea stagnalis lilliance and Galba emarginata in coitu. As the 

 specimens were not preserved to deposit their eggs, the result of the 

 union is not known. 



The eggs of Lymnsea are laid in irregularly elongate-ovate, gela- 

 tinous masses on stones, sticks, stems and leaves of water plants, on 

 other shells, both dead and those occupied by the animal, and, in fact, 

 on any kind of debris. The size of the egg masses varies consider- 

 ably in the same species as do also the number of eggs in each mass. 

 Three egg masses of Galba palustris from Colorado gave the follow- 

 ing data: 



Size 16.00 + 4.50 mill ; number of eggs 50 

 " 19.50 + 4.50 " " " " 64 



" 11.50 + 4.50 " " " " 26 



Galba rcflcxa from Chicago measured as follows : 

 Size 34.50 + 1.60 mill ; number of eggs 130 



The embryology of the Lymnaeas does not differ radically from 

 that of other Pulmonata, excepting in some minor features., notably 

 the retention of the velum in post embryonic life. In the trochosphere 

 a ring is formed about the developing embryo, which becomes ciliated 

 and is used as an organ of locomotion. This is termed the velum, and 

 when fully developed the mollusk is said to be in the veliger stage. 

 The mollusk retains this velum in post embryonic life, though it loses 



1 Nach. Mai. Gesell., I, p. 3S. 

 2 Journ. Conch., IX, p. 282. 



