142 Journal of the Asiatic Society of Bengal. [N.S., XII, 



spring and the autumn being short and ill-defined. The winter 

 lasts from November to March, somewhat longer in the northern 

 than in the southern parts of the Punjab. This part of the 

 year is very cold and practically rainless, except for a few 

 showers in December and January. The daily temperature 

 never rises above 70°F.,butmay go down to 40°F. or even 

 lower. Towards the end of April the summer sets in, and the 

 shade temperature goes up to 90°F., even reaching as high as 

 120°F. in June, remaining so till about the middle of the month 

 of June, when the monsoon breaks and the rainy season begins. 

 The rainy season lasts throughout August and September, du- 

 ring which time the atmosphere, up till now quite dry, becomes 

 very moist owing to an increase in the atmospheric humidity, 

 due to the heavy rainfall, as also an increased evaporation from 

 the surface of the numerous ponds and pools resulting from the 

 rains. The shade temperature during these months slightly 

 falls, and the nights are rather cool. About the middle of Octo- 

 ber the nights become very much cooler, and the shade tem- 

 perature during the day also decreases, till about the end of 

 the month the winter becomes fully established. 



Summing up, one may say that the climate of the Punjab 

 during the winter is like that of most of the European countries 

 and quite different from that of Bengal. During the summer, 

 on the other hand, especially during May, June and July, it 

 closely resembles that of many tropical countries. These clima- 

 tic changes must exercise a very great influence on the aquatic 

 Fauna of the Punjab ; for it is clear, that the severe winter 

 would be quite unfavourable to such animals as flourish in a 

 tropical climate,- while the equally severe summer must be quite 

 detrimental to the animals that live in the temperate zones. 



Dr. Annandale describes the climatic conditions in England 

 on p. 3 of the work already quoted. He contrasts those that 

 affect an Indian pond and points out that the seasonal crisis 

 that takes place annually in the biology of the different species 

 does not occur at the same time of year in the case of all species. 

 With regard to an Indian pond or lake he says : "a similar 

 crisis takes place in the case of most species, but not at the 

 same time of the year in the case of all species. In Bengal 

 some species flourish chiefly in winter and enter the quiescent 

 stage at the beginning of the hot weather (that is to say about 

 March)." The conditions in the Punjab, already described, 

 differ considerably from those that occur in Bengal, the 

 changes being both more sudden and more violent. 



It may be stated that for any observations on periodic phy- 

 sical change only such animals can be selected as adopt any 

 special means of resisting the unfavourable conditions of life 

 for the preservation of the species. 



The forms selected were (1) Hydra oligactis, Pallas; (2) 

 Spongilla carteri, Carter (Bowerbank in Litt) ; (3) Spongilla 



