12 Guide to Insects and Ticks 



21.- — On entry into tlie ovum the microgamete becomes a 

 nucleus. The two nuclei unite, and the fertilised ovum or zygote 

 becomes motile. 



22. — The zygote elongates and bores its way through the 

 wall of the stomach of the mosquito. Ookinete or vermicule 

 stage (fig. 1, A). 



23. — On the outer surface of the stomach of the mosquito the 

 ookinete becomes spherical, and increases greatly in size, the 

 nucleus multiplying at a rapid rate. A protective covering or cyst 

 forms around the sphere. (Only one half of the sphere is shown.) 



24. — The sphere divides up into sporoblasts, each being a small 

 cell with a single nucleus (fig. 1, /). (Only one half of the sphere 

 is shown.) 



25. — In each sporoblast the nucleus divides into a great number 

 of small nuclei, and the surface of the sporoblast growls out into a 

 great number of pointed processes, into each of wdiicli a nucleus 

 enters. These nucleated processes elongate further, and separate 

 from the central part of the sporoblast, and Ijecome motile spores 

 or sporozoites (fig. 1, m). (The model shows only one half of the 

 cyst.) On the bursting of the cyst the sporozoites escape into the 

 various organs of the body of the mosquito. 



26. — Free motile sporozoites. Such of these as reach the 

 salivary glands pass through the ducts of the glands into the 

 proboscis, and when next the mosquito pricks the skin of a man 

 for the purpose of sucking blood, some of them are left in his 

 body, and develop in the red corpuscles in the manner explained 

 by the models in the upper part of the series. 



In the large table-case that stands in Bay YI, on the East 

 side of the main staircase, are shown models of the malarial 

 parasite somewhat similar to those just referred to, but of earlier 

 construction. They illustrate the phases in the life-history of the 

 organism so far as they were known at the time when the models 

 were made (1901) ; the more recent series, in the case near Bay X, 

 embodies the results of investigations up to May 1913. 



On the sloping panels in this table- case in Bay YI are 

 mounted enlarged models ( x 28) of one of the malaria-carrying 

 mosquitoes, Anopheles macHli'pomis Mg., similar to the two models 

 already seen in the other case (Bay X). Side by side with these 

 are shown, for purposes of comparison, enlarged models of another 



