PROTOZOA 187 



2. The Sexual Cycle in the Mosquito. If, now, the blood is 

 shed, certain of the gametes (the male forms or microgameto- 

 cytes) extrude long protoplasmic processes containing a central 

 core of chromatin, and which represent the male fertilizing 

 element (micro gametes] . These become detached, and, entering 

 a female gamete (macrogamete) , a true sexual fertilizing process 

 takes place. In the alimentary canal of the mosquito these 

 fertilized cells penetrate the stomach-walls and form cysts 

 (oocysts) filled with a large number of filiform spores (sporo- 

 zoites), which are extruded into the body cavity of the insect, 

 and some of which reach the salivary glands, whence they are 

 ejected when the mosquito bites. This cycle of development 

 takes seven or eight days. 



Three Forms of Malarial Protozoa. i. The Tertian 

 Form. The adult forms are large, not very refractile, and 

 their outline is somewhat indistinct. There is an abundance 

 of fine pigment-granules, and the ameboid motion is vigorous. 

 Segmenting forms divide into fifteen to twenty merozoites; the 

 sexual forms or gametes are large. The red cell containing the 

 organism is swollen and pale. Sporulation and, therefore, the 

 malarial paroxysm occur every forty-eight hours. 



2. The Quartan Form. The organism is smaller, is more 

 refractile, and its outline is more distinct. The pigment is 

 coarse and situated at the periphery of the organism, while the 

 protoplasmic motion is sluggish. Segmentation forms only 

 six to twelve spores, and has the regular "daisy-head" appear- 

 ance; the gametes are small. The red cells become dark in 

 color, and the cycle requires seventy-two hours. 



3. Estivo -autumnal Form. The adult forms are found 

 mainly in the spleen and other viscera, and do not very often 

 occur in the peripheral blood; their outline is sharp, and they 

 are highly refractile. The pigment is scanty and fine; the 

 motion is active. A variable number of merozoites is formed 

 usually six to twelve. The gametes are characteristic, being 

 crescentic in shape and very resistant to quinin. The red cell 

 becomes shriveled and yellowish. The cycle usually takes 

 forty-eight hours, though it is somewhat variable. 



