74 Journal of the Asiatic Society of Bengal. {January, 1913. 
the case in much warmer weather if the water were deeper. 
The water-level of the Lake of Tiberias is lower in October 
stones that are partly or completely dry. I made a very 
careful study of those that had become desiccated or partially 
desiccated in this way, and I found that whereas Ephydatia 
had produced gemmules, NV. mappa had not done so. Changes 
in environment, as I have pointed out elsewhere,! do not 
necessarily have the same effect on di 
bable that WN. mappa, 
mules, would do so whe 
steady desiccation. 
Evidence, moreover, is accumulating that the adoption of 
a limnic as distinct from a fluviatile mode of life is liable to 
(vars. abortiva and 
or less degenerate. 
‘|! Faun. Brit. Ind., Freshwater Sponges, etc., p. 5 (1911). Journ. 
As. Soc. Bengal, 1912, p. 50. 
2 Proce. Roy. Irish Acad., xxxi, pt. 60, p. 64 (1912). 
5 Proc, Acad. Nat. Sci. Philadelphia, 1887, pp. 191, 192, 
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