FLAGELLATED ORGANISMS. 521 



this view, and has found that in the stomach of the 

 mosquito many of the crescents become spherical, and 

 develop into the flagellated forms. Furthermore, in the 

 case of certain mosquitoes when allowed to suck malarial 

 blood there appear in the walls of the stomach certain 

 rounded cells containing pigment like that seen in the 

 malarial parasite in the blood. Beyond this stage he has 

 not yet traced the development of the malarial parasite in 

 the mosquito, but he has done so in the case of the 

 proteosoma infection of birds above referred to. The 

 stages of development, which are of a highly interesting 

 character, are as follows. 



On the second day after mosquitoes have been allowed 

 to suck the blood of infected birds there appear in the 

 walls of the insects' stomachs small oval pigmented bodies, 

 chiefly situated between the muscle fibres. These bodies, 

 which measure at this stage about 6 //, in diameter, rapidly 

 increase in size, so that on the fourth or fifth day they may 

 reach a diameter of 60 //, and may cause little bulgings on 

 the outer wall of the stomach. They have a well-defined outer 

 capsule, and their protoplasm shows finely striated mark- 

 ings ; they may be called coccidium cysts. The cysts in 

 .course of time burst and set free in the body cavity an 

 enormous number of minute spindle-shaped and somewhat 

 curved rods " germinal rods." These rods are carried to 

 various parts of the body and are especially taken up by 

 the epithelial cells in a branching gland at the base of the 

 insect's proboscis. The striking result has been obtained 

 that when a mosquito with the rods in this position is 

 allowed to bite a healthy bird the latter becomes infected, 

 and the proteosoma appears in large numbers in its blood 

 after an incubation period of six or seven days. These 

 experiments which have thus resulted in tracing the life- 

 history of this parasite, have been carefully checked by 

 controls and have also been recently confirmed in all 

 essential details by the observations of Koch on the same 

 parasite. There can be little doubt that a similar cycle, the 

 earlier part of which has already been observed, will be 



