THE SPOROZOA 



249 



The latter author describes the conjugation and fusion of ring-stages in 

 pairs within the blood-corpuscles. Wright [98] also supports the view that 

 the crescents arise from a syzygy of amoebulae within a doubly-infected 

 corpuscle. The analogy of the life-histories of other Haemosporidia or 

 Sporozoa affords no support to these statements, and the appearances upon 

 which they are based might equally well be interpreted as stages in the 

 fission of an amoebula or young gametocyte. Recently Schaudinn [94a] 

 has traced all stages in the development of the gametocytes of the tertian 

 parasite from the merozoites, so that the notion that the former arise 

 from fusions of amoebulae must be regarded as an exploded idea. 



The intermediate host necessary for the propagation of the parasites 

 of malaria in man is a gnat or mosquito, belonging to the genus 

 Anopheles. Up to the present no other means of propagating the 

 disease has been discovered than through the agency of these insects. 

 If a human being suffering from malaria is bitten by an Anopheles 



FIG. 69. 



Anopheles clai'iger, Fabr. (After 

 Grassi.) X about 4. 



FIG. 70. 



Diagrams to show the positions assumed 

 when at rest by a, Anopheles; b, Ovlex. 

 (After Neveu-Lemaire.) 



mosquito (it is only the female gnats that suck blood), the mosquito 

 draws into its stomach various stages of the parasite along with the 

 blood. Young amoebulae, full-grown schizonts, rosettes, crescents, all 

 alike may be swallowed by the mosquito, but with different results. All 

 stages of the schizogonous cycle are digested in the mosquito's stomach 

 along with the blood corpuscles. The gametocytes alone are able to 

 resist the action of the digestive juices, and to continue their develop- 

 ment further. Freed from the last remnants of the blood-corpuscle in 

 which they grew up, they assume the spherical form, if they have not 

 already done so, and proceed to give rise to the gametes. The maturation 

 of the gametes and their subsequent conjugation take place in the 

 stomach of the mosquito. 



The relation of the Haemosporidia to their intermediate hosts is one 

 of those finely-adjusted bionomical adaptations so frequently observed in 

 the life-histories of parasites. For if a malarial patient be bitten by a 

 mosquito of any other genus than Anopheles by a species of Culex, for 

 example then not only the schizonts, but also the gametocytes, are 



