286 



THE PROTOZOA 



mn o 1 



the pigment is clumped rather than in belts or lines as with aestivo-autumnal. 

 Darling has also noted that mosquitoes do not tend to become infected unless the 

 gamete carrying man has more than 1 2 gametes to the cubic millimeter. 



The capsule of the mature zygote ruptures about the tenth day and the sporo- 

 zoites are thrown off into the body cavity. They make their way to the salivary 

 glands and thence, by way of the veneno-salivary duct, in the hypopharynx, they are 

 introduced into the circulation of the person bitten by the mosquito, and start a 

 nonsexual cycle. As the sexual life takes place in the mosquito, this insect in the 

 definitive host and man is only the intermediate host. The cycle in the mosquito 

 takes about ten to twelve days. 



e 



forms in Man 

 ~ Gametes 



>/oheline mosquito (definitive 

 n eriod tcLsts Q-/odays 

 t 25' 'to 30" C. 



-sexua/ cyc/e f 

 \jn man (inter- \ Q ' 

 J^ mediary Aostjo o 



^ ,. 



-cg 



FIG. 63. Sexual (sporogony in mosquito) and non-sexual (schizogony in man) 

 cycle of the malarial parasite. The sporogony diagram to the left shows in lower 

 portion the fertilization of the female gamete by the microgamete. The vermiculus 

 stage of the zygote is shown boring into the walls of the mosquito's stomach to later 

 become the more mature zygote packed with sporozoites as shown in the upper dia- 

 gram of the developmental processes in the mosquito's stomach. 



Efficient Mosquito Hosts. It must be remembered that only certain 

 genera and species of Anophelinae are known malaria transmitters; 

 thus Stephens and Christophers, in dissecting 496 mosquitoes of the 

 species M. rossi, did not find a single gland infected with sporozoites. 

 With M. culicifacies, however, 12 in 259 showed infection. A 

 mosquito which is capable of carrying out the complete sporogonous 

 cycle is an efficient host and in the case of malaria the mosquito is the 

 definitive host (sexual life of parasite). 



Malarial Index. Mosquito dissection is one method of determining 

 the endemicity of malaria or the malarial index. There are two other 

 methods: i. by noting the prevalence of enlarged spleens, and 2. by 



