33 



lively and agile; after 5 minutes' exposure the insect was dead. I then 

 substituted another tube containing a Culex mosquito, and after leaving 

 it exposed to the sun during 15 minutes it was still alive and continued 

 to live another 24 hours in its tube. 



It is well known that only the female mosquitoes bite and suck blood, 

 while the males feed en vegetable juices, principally the sweet ones; but 

 I have not found it mentioned in any author that even the females never 

 bite before having been fertilized. This, at least, I infer from the follow- 

 ing experiments: 



A female C. mosquito, caught soon after breaking loose from its 

 puppa-case, and kept alive during three days, cannot be got to bite during 

 that space of time. I have several times repeated the experiment and 

 always with a negative result. 



Female mosquitoes which are caught pairing bite and suck blood 

 readily very soon after they are parted. 



Finally, those which are caught in the act of biting and sucking 

 blood, will as a rule, lay eggs after a few days, while the fertilized 

 females which have not been allowed to suck blood die without ever 

 laying any ova. 



We are thus led to infer that the craving of the female mosquito 

 for live blood is not meant to supply au indispensable article of food. 

 Indeed it seems improbable that for the nourishment of so small a body, 

 such a disproportionate quantity of rich blood should be needed. I 

 have come to the conclusion that the sucking of blood is intended for 

 another object connected with the propagation of the species. The 

 likeliest hypothesis seems to be that the feed of blood acts through the 

 degree of heat which it procures. If, for instance, the maturation of the 

 ovules contained in the ovaries of the mosquito demands a temperature 

 of 37° C, the latter could scarcely be obtained by any other means 

 so readily as by the insect filling itself with a fair amount of blood of 

 that temperature ; and sometimes it may be more convenient for the 

 mosquito to bite a patient attacked with fever, whose blood at 39° or 

 or 40° may prove more efficacious in hastening the process of ovulation. 

 It will thus be understood why large insects like the zancudo are able 

 to absorb with a single bite the amount of blood required for the matu- 

 ration of all the 200 to 350 ova which they lay at one sitting, while the 

 smaller species, like the C. mosquito, have to bite and fill themselves 

 several times with blood before beginning to lay, and generally require 

 several sittings before all their ova are laid. 



After the female mosquito has filled itself with blood it requires 

 two, three or four days, according to the species (and the season of the 

 year) to complete the digestion of its feed; and, during that time, re- 

 mains out of sight spending hours in a curious performance the object 



