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15. BIONOMICS OF ANOPHELES LARV. 
We made the following observations: 
(1) Eggs.—These are boat-shaped, like those of Anopheles observed in India. They 
appear to be laid singly on water, but cohere by their ends, forming typical triangu- 
lar patterns, and also adhere to floating objects, the sides of the vessel, ete. We 
observed no facts indicating that they are ever laid on solid surfaces. Jn vitro they 
take about twenty-four hours to hatch, but the period is probably much shorter in 
es 
(2) Duration of larval stage.-—This depends on temperature and amount of food. 
Gales natural conditions it may probably be only three or four days, but under unfa- 
vorable conditions (cold, overcrowding, absence of food) it may certainly extend to 
weeks. There are reasons for thinking that development is much hastened by 
bright weather, in order to enable the imago to hatch out before desiccation of the 
containing puddle. 
(3) Food.—The larve were frequently watched floating on the surface and feeding 
on filaments of waterweed, amongst which they often entangle themselves. On dis- 
section the intestine was found crammed with these filaments. It was observed that 
in vitro the larvee scarcely grow in size unless they are given large quantities of water- 
weed, which they dispose of very rapidly. On the other hand, larve were often 
caught in puddles in which no green vegetation could be seen. They may eat other 
food, but it would seem as if waterweeds constitute their favorite diet. It was also 
noted that they obtain shelter among these weeds from the current running through 
the pools during or after rain. 
(4) Enemies.—No observations could be made under this head, but we often found 
many frogs and tadpoles in the breeding pools, apparently living at peace with the 
larve. 
(5) Hfects of desiccation.—During most of our stay in Freetown heavy showers fell 
several times a day, so that the larve could live secure from desiccation in all but 
the most evanescent puddles. In September, however, there was a complete break 
in the rains, lasting three days. A large number of the pools, even many of those 
containing waterweed, and those fed by springs during rain, dried up completely. 
The question whether the larve had the power of living in the mud at the bottom of 
the pools could now be tested by direct observation. The break in the rains was 
followed by heavy showers, which immediately refilled all the puddles. Had the 
larye continued to exist in the mud, they would now have emerged again. As 
regards the puddles in which the mud had completely dried, this was not the case. 
No larvee at all were found in them for at least two days after the rain had refilled 
them. After that interval larve again appeared, but they were very small ones, 
evidently just hatched from the egg. On the other hand, it was frequently 
observed that if the mud did not become completely dry, the larve would emerge 
into active existence after another shower. These observations were supported by 
some experiments in vitro, and we therefore conclude that the larve can withstand 
partial, though not complete, desiccation.’ 
(6) The same puddles constantly occupied.—We have suggested (paragraph 13) that 
the position of the breeding pools may change according to the seasons, but while we 
were in Freetown there was no change of season, and we generally found Anopheles 
larvee in the same puddle, namely, in those which were suitable for them. Thus, of 
two puddles lying close together, one would never contain larye and the other 
would always contain them. The explanation of this probably is that the larvee 
1One of us kept Culex larve alive for two months in a bottle in the cold weather in 
India. 
2 One of us reared adults from full-grown larvee ken on damp blotting paper (in 
India), but found that the young larvee died when kept under these eomditionk: 
+ ae 
BE Latin 4 6 
