90 AN INTRODUCTION TO ZOOLOGY 



called melanin (9 and 10, p.) ; these are waste matters that have 

 accumulated during the growth period, being modified products 

 of the digestion of haemoglobin. 



Reproduction now takes place by a p ocess termed schizogony 

 (I-V and 6-10), the parasite after it enters the blood corpuscle, 

 being known as a schizont. During this process the nucleus 

 divides a number of times without the intervention of cell walls 

 until from twelve to sixteen daughter nuclei are present (8). 

 Each nucleus, with part of the surrounding cytoplasm, is then cut 

 off from its fellows, resulting in the production of a number of 

 small cells, called merozoites, inclosed in the membrane of the 

 corpuscles (9). The melanin granules are not included in the 

 daughter cells, but remain in the center of the mother para- 

 site (9, />.). The merozoites finally break through the walls of 

 the corpuscle and escape into the blood plasma. The melanin 

 granules are also liberated at this time (10, />.); they are car- 

 ried by the blood to the liver, kidney, spleen, lungs, or brain, fre- 

 quently resulting in the pigmentation and hypertrophy of these 

 organs. An attack of fever coincides with the liberation of the 

 merozoites, and the interval between the penetration of a blood 

 corpuscle and the production of merozoites is termed the period 

 of incubation. This period in Plasmodium vivax, as stated above, 

 is forty-eight hours. All the merozoites simultaneously attack 

 other corpuscles (10 to I), producing the chill which is a symptom 

 of malaria. 



Several asexual cycles like that just described are passed 

 through; but finally, for some unknown reason, the merozoites 

 develop into sexual phases (VI-XII). Part of them, named 

 macrogametocytes (VII, b.) become capable of producing a single 

 female gamete or macrogamete (X, b.), while the rest become 

 microgametocytes (VII, a.) , each capable of producing as many as 

 eight male elements or micro gametes (X, a.). The gametocytes 

 cannot produce gametes within the human body but must first 

 be sucked up into the alimentary canal of an Anopheles mosquito. 

 Here all stages of the parasite except the gametocytes are di- 



