REPORT ON MOSQUITOES. 67 



This purely asexual mode of reproduction by spores may go 

 on in the blood for a long time; but not indefinitely. Sooner or 

 later some of the plasmodia assume an appearance different from 

 the rest. The difference is but slight in the tertian and cpartan 

 fevers ; but in the sestivo-autumnal it is striking. In this forrn of 

 malaria the plasmodia assume a semi-lunar form and are known 

 as 'crescents.' A general name now applied to all these bodies 

 is "gamete" or "gametocyte."' On drawing a little of the blood 

 in which these bodies occur and watching them closely under the 

 microscope, some of the gametes distinguishable by slightly larger 

 size will suddenly be seen to give birth to several actively lashing 

 thread-like bodies, known as the flagella or microgametes. "These 

 swim actively through the blood serum, and finally unite with 

 other gametes which have remained inert, producing no flagel- 

 lated bodies. The union of these two bodies — the inert macro- 

 gamete and the tiny, active microgamete — constitutes the process 

 of fecundation. It is essentially the union of the male element 

 (spermatozoan) and the female element {egg or ovum), which 

 everywhere inaugurates the development of a new being. Only 

 in the case of the malarial organism we have to do with a uni- 

 cellular parasite, and one perfectly adjusted to a very special mode 

 of existence. It was soon ascertained that 'exflagellation' (and 

 consequently fertilization) never occurs until the blood has been 

 drawn ;" but it may occur anywhere else outside the human 

 body. 



In other words, within the human blood only the vegetative 

 reproduction by spores can take place. When the gametes are 

 produced they persist in the circulation for an indefinite period 

 without chang-e; but when removed, as by the bite of an insect, 

 development begins at once. So far as we know it matters not 

 what the biting insect is — ^whether fly, bug, mosquito or flea — 

 flagellation and conjugation will take pace. This, however, is 

 the limit to^ which development can go in places other than the 

 stomach of an Anopheles mosquito. If the patient be now bitten 

 by such a mosquito and some of the gametes absorbed \\ith the 

 blood, fertilization (figure 15, 6) takes place and the sexual 

 cycle begins. "As the first result we get a httle, worm-like body, 

 the ookinet or vermicule, which works its way into the wall of 

 the mosquito's stomach. The stage, shown in fig. 15, 8, is passed 

 in the wall of the stomach. The subsequent stages, character- 

 ized bv very rapid growth, occur apparently on the outside ( i. e., 

 the peritoneal surface) of the scomach; but, actually, just under 

 the extremely thin, muscular and elastic layer, which is very 

 distensile and stretches tO' accommodate the growth of the para- 

 site. These large bodies soon become visible on the stomach of 



