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



the Sponges and Polyzoa sexually, to produce new independent 

 individuals, and asexually, to form large colonies by prolifera- 

 tion, so that during this time the number of individuals may 

 increase as much as possible. With the coming on of unfavour- 

 able conditions all these at once begin to produce the resistent 

 bodies which are capable of lying dormant till the return of 

 the more favourable weather. As on the approach of un- 

 favourable conditions the number of individuals for the pro- 

 duction of the resistent bodies is very large, a large number 

 of such bodies is produced ; and even though the individuals 

 and a large number of these resistent bodies may perish, yet 

 the race will be preserved, and with the return of favourable 



conditions a large number of new individuals will at once 

 appear. 



In the case of Daphnia it was seen that the individuals had 

 the "winter eggs' 9 in the brood-pouch in January. I have also 

 taken individuals with such fertilized eggs from other places in 

 February and March; in these cases the individuals were dead 

 and there was a single egg in the brood pouch of each. Speci- 

 mens of Daphnia taken in summer on the other hand had no 

 eggs ; they were probably breeding by means of unfertilized 

 parthenogenetic eggs ; but I am not in possession of further ob- 

 servations on this head. 



The insect larvae that were regularly observed this year were 

 those of three species of Chironomidae and of two species of the 

 Anopheles mosquito. In the case of these insect larvae resis- 

 tent bodies like the gemmules of sponges are not produced, with 

 the advent of the unfavourable conditions ; on the other hand 

 it was found that the period during which a larva would be 

 transformed into a pupa, and the latter into the imago, is very 

 much increased, owing to the decreased vitality of the larva, 

 due directly to the cold weather. To prove this experimentally 

 a small jar containing the larvae of Chironomus was kept in an 

 incubator at 90°F., when it was seen that these ' ' blood-worms 

 became very active and pupated in three days ; as a control 

 experiment some others were kept exposed to the ordinary 

 conditions, and it was seen that practically no change had taken 

 place during this time and that the larvae were lying quietly 



win 



ever towards pupation. That the laboratory conditions had 

 not brought about this change in any way was further proved 

 by the larvae in open ponds being in the same condition and 

 by the adult fly of Chironomus being quite scarce at this time. 

 A similar condition was observed in the case of the larvae and 

 adults of Anopheles. 



It may be suggested here that this would really be the time 

 to plan a campaign for the destruction of the mosquitoes, it- 

 larvae and the breeding places, for, owing to the much smaller 

 number of breeding places and the inactivity of the mosquito 



