306 Sporozoa 



of Haemoproteus often divide into meroblasts, each of which grows be- 

 fore producing merozoites. However, the formation of meroblasts may 

 be skipped. Gametocytes of Haemoproteus develop in erythrocytes and 

 deposit cytoplasmic pigment comparable to that of malarial parasites. 

 Young gametocytes of L. simondi appear in lymphocytes, monocytes, 

 myelocytes, and late polychromatophil erythroblasts (53); only those in 

 the red cells deposit pigment in their cytoplasm. The Haemoproteidae 

 of birds undergo syngamy and sporogony in blood-sucking flies (Lynchia, 

 Simulium, and related genera) which ingest gametocytes from the blood 

 (1, 48, 102, 103). 



The family includes Haemoproteus Kruse (52, 102; Fig. 6. 22, A-H) and Leucocyto- 

 zoon Danilewsky (53, 138; Fig. 6. 22, I, J). Checklists of species and host indices are 

 available for Leiicocytozoon (19), Haemoproteus (18), and for species of both genera 

 found in North American birds (47). 



Family 2. Plasm odiidae. This family includes one genus, Plasmodium 

 Marchiafava and Celli (Figs. 6. 20, 21), which includes malarial parasites 

 of reptiles (130, 131), birds (49), and mammals. Check-lists and host- 

 indices are available for the genus (20) and for species parasitic in North 

 American birds (47). Species causing malaria in man are discussed in 

 Chapter XIII. 



Order 2. Babesiida. The life-cycles are not yet completely known. Non- 

 pigmented stages, in the red corpuscles of cattle and certain other mam- 

 mals, are ingested by ticks and establish infections in these invertebrate 

 hosts. With the demonstration by Smith and Kilbourne (123), that ticks 

 transmit Babesia bigemina, arthropods were identified for the first time 

 as vectors of protozoan parasites. 



One of the most completely known life-cycles is that of Theileria pai~ua 

 (21, 22; Fig. 6. 23), which causes African Coast fever of cattle. Erythro- 

 cytic stages are ingested by a tick and liberated in the gut. Small parasites 

 of two sizes are soon observed, usually in clumps, and syngamy is be- 

 lieved to occur. Larger parasites (Fig. 6. 23, A), believed to be zygotes, 

 now replace the ones which first appeared in the tick. After preliminary 

 growth, an elongated ookinete is developed within the zygote. Such 

 ookinetes appear later in the body cavity near the salivary glands and 

 some of them enter gland cells (Fig. 6. 23, B-D). The ookinete now rounds 

 up and produces a number of sporoblasts, each of which divides into 

 sporozoites (Fig. 6. 23, E, F). The sporozoites escape into the salivary 

 ducts and are inoculated into the mammalian host when the tick begins 

 to feed. Sporozoites pass by way of lymph vessels to a lymph gland, and 

 the survivors invade lymphocytes where they develop into multinucleate 

 schizonts (Fig. 6. 23, G), or "agamonts" (21). As the infection progresses, 

 so-called gamonts appear. These stages stain less intensely and have 

 smaller nuclei than those of the agamonts. Multinucleate gamonts (Fig. 



