ELISHA MITCHELL SCIENTIFIC SOCIETY. 7 1 



On the 1 6th three thick nidamenta of some forty eggs 

 each were seen loosely attached to the walls of the glass 

 aquarium. A few days later four others had been depos- 

 ited. Up to June 15th the aquarium was examined at 

 intervals nearly every day. iVfter that date it was not seen 

 again until July 12th, when the water was changed. The 

 next day both the snails were dead, probably as the result 

 of the change of water. 



In the period of four months — say ]\Iarch 12th to July 

 I2i:h — the pair produced 43 nidamenta, w^hich contained, 

 on an estimate certainly not too high, an average of 30 

 eggs each. So that the number of their offspring for the 

 period mentioned amounted to 1,290. There w^as ho well- 

 marked decline of the reproductive function toward the 

 close of the period, w^hich is perhaps another indication 

 that they came to their death by violence. 



From March 31st to June 6th inclusive, the pair were 

 observed in coitu as many as 15 times, at hours ranging 

 from 8:30 A. M. to 6:15 P. M., the coitus lasting sometimes 

 but 20 minutes, sometimes more than an hour. The male 

 function was performed alternately by the two snails. The 

 eggs appear to have been laid only during the night.* 



It was important to determine, if possible, the age at 

 which sexual maturity is attained and reproduction begins. 

 Accordingly, on the 12th of July I took out of the aqua- 

 rium two of the largest of the young snails and put them 



*It may be mentioned, however, in view of the similarity of the habits of Phj-sa and 

 of Limnceus, that I once observed a specimen of the latter depositing a nidamentum 

 on the glass wall of the aquarium at 2:20 p. m. The work was about half done when 

 it caught my e^-e, and I judge that tv/o minutes were consumed in completing it. The 

 eggs and the protecting jelh- emerged at the same time from under the right side of 

 the shell aperture and at right angles to its margin, the snail moving slowly sidewaj-s 

 in the opposite direction. When the nidamentum was completed, the snail turned 

 slowly round on the glass, made tv.-o or three rather aimless grazing movements of the 

 mouth, and then crawled slowly over the nidamentum in the direction of its longer 

 axis, completely covering it v/ith the foot. That position was maintained but a mo- 

 ment or tv.-o; nevertheless the snail remained near by. When I. lightly touched the 

 nidamentum and the snail at the same time, the latter shrank a little, but immediately 

 proceeded to cover the threatened nest. During the fifteen minutes that I watched 

 further, the snail remained close to the nest — with the view of protecting it ? I thought 

 I detected that the jelly of this one freshly made was somewhat softer than that of an 

 older one near by. 



