No. 465.] ZNTERRELATIONSHIPS OF SPOROZOA. 617 
This order is, in some respects, the best studied of all the Spor- 
ozoa, since it numbers amongst its members the parasites of 
malaria and yellow fever. In the acquisition of two hosts, it 
reaches a higher degree of specialization than the Coccidia, and 
extreme specialization is also indicated by the relative paucity in 
species. It is to be remembered, however, that from the bio- 
logical side, the group is not so well known as either the Coccidia 
or the Gregarinida. Accordingly, generalizations valid to-day 
may need to be modified as our knowledge increases. 
Two suborders have been established, the Haemosporea and 
the Acystosporea. With the exception of one important fea- 
ture, the life history of these two is the same. It is further 
essentially the same as that of the Coccidia. 
^ Asin the rest of the Telosporidia, the Haemosporidian begins 
its career as a sporozoite. Set free in the blood of the host, 
this sporozoite attacks and enters a blood cell, preferably an 
erythrocyte. Here it grows into a trophozoite, which is amoce- 
boid in the Acystosporea and generally vermiform in the Haemo- 
sporea. The trophozoite, growing at the expense of the blood 
cell, soon breaks up into a number of merozoites. By the dis- 
integration of the blood cell, the merozoites fall into the blood 
stream. Forthwith they attack new blood cells and the process 
(schizogony) is repeated. The increase is therefore by geomet- 
rical ratio and as Minchin says: “It is evident that reproduc- 
tion at this rate could only continue indefinitely in the ichor of 
an infinite host.” Accordingly, at the end of a certain number 
of generations, the parasite provides for its future by the pro- 
duction of male and female elements. 
So far the process is exactly parallel to that found in the Coc- 
cidia: In the Haemosporidia, however, or rather in the Acys- 
tosporea, the male and female cells must be removed from the 
blood of the host to insure further development. This removal 
is effected by a blood-sucking insect (a mosquito) which takes 
the parasites into its alimentary canal. Here they mature, the 
male cells forming each a number of microgametes, the female 
cells each a single macrogamete or egg. The microgametes 
fertilize the macrogametes, which then metamorphose into 
elongated elements, the oókinetes. The oökinete pierces the 
