POLYVITELLINY IN POND SNAILS. 



321 



Of a large number of Lynincea columella eggs taken at random 

 only one contained more than one vitellus. This egg had two, 

 one of which died in early cleavage and the other reached the gas- 

 trula stage. 



Three F 1 and six F. 2 of snail number 5, Table I., deposited a 

 number of masses, which are not recorded in Table I., but none 

 contained polyvitelline eggs. 



Polyvitelline eggs occur most often in those masses which con- 

 tain a large number of eggs (i.e., 70 to 150 in L. s. appressu}, and 

 large masses are deposited by large, old individuals in the prime 

 of life more often than small masses. This fact and the com- 



TABLE I. 



NORMAL AND POLYVITELLINE EGGS LAID BY TWENTY Lymncea stagnatis appressa. 



Individual snails designated iFii iFi6 are Fi progeny of snail No. i. Likewise, 

 those designated 4Fii, sFii and 5F:2 are the Fi progeny of snails No. 4 and No. 5. 

 Snails Nos. 1-4 and n were adults when collected from lakes near Ann Arbor, 

 Michigan, while all the others were reared in the laboratory. All the Fi individuals 

 and those numbered 6-10 inclusive were reared in isolation. The masses for each, 

 individual are consecutive. 



