1146 Proceedings of Royal Society of Edinburgh. [sess. 
of these females contained 4-5 parthenogenetic eggs ; young ones are 
still rather common, and so are the males and the big females con- 
taining 8-12 eggs. On 16th October almost all the small-sized 
Fig. 4. — 15th July, 
big female, eight young ones. 
Fig. 5. — 1st August, 
young female. 
females have ephippia, the males are rare and there is very little 
brood ; the large females are still rather common and contain 7 -9 eggs. 
The above-mentioned facts may, I think, best be explained as 
follows : As the number of animals to be found on 30th May,, 
only two days after the ice has broken up, is extremely small and 
continues so the whole of June, I suppose that almost all the 
individuals of the lake have hibernated in ephippia. As the 
