MORPHOLOGY AND TAXONOMY OF THE SPOROZOA 543 



Taliaferro (1924) estimate about 150,000,000 parasitized blood 

 elements at this time in the case of human malaria, all parasites, if 

 derived from a single infection, undergoing sporulation at practically 

 the same time and liberating their toxin simultaneously into the 

 blood. The pyrexia! attacks of chills and fever in human malaria 

 are thus accounted for. Ultimately the agametes develop into 

 gamonts which are usually easy to distinguish from the agamonts 

 and which are frequently differentiated into macrogametocytes and 

 microgametocytes. The gametocytes are taken with the blood 

 into the digestive tract of an invertebrate host (mosquitoes) where 

 the microgametes are formed and where union of gametes occurs. 

 The zygote, like that of some hemogregarines, is motile and makes 

 its way by gregariniform movement to the wall of the gut. These 

 motile zygotes, termed ookinets by Schaudinn, either enter the 

 epithelial cells of the gut or penetrate them and come to rest against 

 the inner membranes of the gut wall. Here a delicate sporocyst 

 membrane is formed and the amphinucleus divides repeatedly with- 

 out cytoplasmic division until a vast number of nuclei results. The 

 cytoplasm then divides to form as many naked sporozoites as there 

 are nuclei. The delicate sporocyst membrane is ruptured and the 

 sporozoites are liberated into the body cavity from which they are 

 passed into the blood of the vertebrate and the cycle repeated. 



The life cycle of the hemosporidian thus has many points of 

 resemblance to that of the coccidian ; the same intracellular mode of 

 life, the same asexual generation and agamete formation, the same 

 formation of gametocytes and dimorphic, gametes. The micro- 

 gametes, however, have no flagella, as a rule, but move like spiro- 

 chetes and the zygote, as noted above, forms naked sporozoites. 

 In many cases, however, there is a reminiscence of sporoblast forma- 

 tion, when, after the amphinucleus has divided for a certain limited 

 number of times, the cytoplasm separates into a number of sporo- 

 zoite-forming centers. The resemblance to the coccidian would be 

 complete if such centers were provided with definite capsules. 



The two families — Hemoproteidae and I'lasmodiidae — differ in 

 the site of asexual multiplication. In the former the schizogony 

 cycle occurs in endothelial cells, the merozoites ultimately entering 

 red blood cells of birds where they develop pigment and grow into 

 gametocytes. These are ingested by a biting fly (e. r/., Lynchia) 

 in which fertilization and sporozoite formation occur in the stomach 

 and body cavity. In Plasmodiidae schizogony occurs in the eryth- 

 rocytes of mammals and birds. 



Sub-order 3. Babesiina. 



These are parasites of red blood corpuscles of mammals which 

 differ from Hemosporidiina by the absence of melanin pigment. 



