294 



PLASMODROMATA AND SARCODINA 



into a new host of the same species as before, when schizogony 

 begins again. 



The changes which the parasite has to undergo in spreading 

 from one host to another are generally associated with sexual 

 reproduction, and the whole cycle from a given host of a certain 

 species to another host of the same species is called the cycle of 

 sporogony, or, more simply, sporogony (Figs. 44, 45, and 46). 



m 



Fig. 44. — Sporogony of Plasmodium vivax Grassi and Feletti. 

 Development of the Microgamete. (After Schaudinn.) 



I, Young microgametocyte ; 2, 3, older forms; 4, fully grown microgameto- 

 cyte> as seen in the blood of man; 5, division of the nucleus (reduction) in the 

 stomach of an anopheline ; 6, nuclei have travelled to the periphery, which has 

 grown out to form the commencement of a microgamete; 7, microgametocyte 

 with three microgametes ; 8, a free microgamete. 



In adverse or changed circumstances, therefore, the merozoites 

 develop into more resisting forms, which are called gametocytes, 

 in which, by reduction of the nuclear material, the male and female 

 elements in the nucleus are separated; the two elements may exist 

 in the same cell or in separate cells, but usually the male element of 

 one cell fuses (zygosis) with the female element of another cell, 

 and forms a new individual with a new nucleus or synkaryon. 



Fig. 45. — Sporogony of Plasmodium vivax Grassi and Feletti. 

 Development of the Macrogamete. (After Schaudinn.) 

 1-2, Young macrogametocytes ; 3, fully developed macrogametocyte in 

 the blood of man; 4, reduction and formation of a polar body in the stomach 

 of an anopheline mosquito ; 5, macrogamete and one polar body. 



This new individual proceeds to reproduce itself rapidly by either 

 binary fission or spore-formation. In the latter case, in order to 

 prevent confusion, the terms employed are different from those 

 used in asexual reproduction. The parasite is called a sporont, the 

 spores sporozoites. The sexual reproduction takes place in the 



