PROTOZOA 201 



2. The Sexual Cycle in the Mosquito. The common mos- 

 quito is known as Culex and does not harbor the malarial 

 parasite. The anopheles species, spotted wings, is the true 

 host; only the females are bloodsuckers and responsible for 

 the spread of the disease. They take the infected blood 

 containing the male element and which represents the male 

 fertilizing element (micro gametes). These become detached, 

 and, entering a female gamete (macro gamete), 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 (sporozo'ites), which are extruded into the 

 body cavity of the insect, and some of w r hich 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. Plasmodium 

 Vivax, or 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. Plasmodium Malaria, 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. Seg- 

 mentation forms only six to twelve spores, and has the regular 

 " daisy-head" appearance; the gametes are small. The red 

 cells become dark in color, and the cycle requires seventy- 

 two hours. 



3. Plasmodium Falciparum, or Malignant Tertian, or Estivo- 

 autiimnal 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 



