SPH^RIUM. 13 



ing, while the adults made many ineffectual attempts ; 

 but both fry and adults^ when they reach the edge of the 

 water, take to the surface easily_, and creep along slowly, 

 and apparently with caution, as if in search of some 

 floating substance, near which they will rest for hours. 

 The exserted foot moves, during this under-surface pro- 

 gression, by a gentle vermicular action, the siphons being 

 at the same time protruded. The foot during repose 

 is usually retracted, and does not seem necessary for 

 mere floating-purposes/^ And he adds, " An inter- 

 esting little scene occurred in the globe the other even- 

 ing. Several individuals had reached a few leaves and 

 hanging roots of minute water-plants which floated in 

 the centre of the globe, down the stems of which three 

 or four had crept to a depth of about an inch and a half. 

 There they reposed : but they were not absolutely mo- 

 tionless ; for, to my surprise, the whole group, plants and 

 all, were dreamingly enjoying the delights of a slow but 

 long- continued rotation. At first I thought some mi- 

 nute water-insect had found its way unbidden into the 

 globe, and was thus illustrating, like some learned lec- 

 turer to his sleepy audience, the laws of planetary mo- 

 tions. But no such lecturer was there : yet, as the 

 revolution brought two of the little moUusks closer under 

 inspection, I observed their siphons to be curved exactly 

 in the opposite direction to the line of motion. Here 

 was a solution at once of the nymph-like aTp6^i\o<i, 

 which was evidently due to the recoil consequent upon 

 the circulation and expulsion of the water through the 

 siphons. The fortuitous position of the two individuals 

 and the combined action of their expulsive tubes may 

 not occur again ; but the whole incident was so inter- 

 esting and remarkable that I could not help recording 

 it. The fry are growing rapidly ; and I opine the 



