RHIZOPODS, ACTINOPODS, SLIME MOLDS, SPOROZOA 93 



develop into gametocytes which are infective for a mosquito. In 

 the gut of the insect, asexual cells are digested but gametocytes 

 produce gametes and fertilization occurs. The motile zygote 

 invades the host tissue, grows, becomes multinucleate and pro- 

 duces many sporozoites which migrate through the mosquito 

 some of them reaching the anterior digestive tract whence they 

 may be injected into the vertebrate. 



Electron-microscope studies of Plasmodium species parasitic in 

 birds and mammals have been reported. Parasites during feeding 

 and reproduction in the vertebrate are described by Fulton and 

 Flewett (1956), Rudzinska and Trager (1957, 1959, 1961), 

 Rudzinska, Bray and Trager (1960), Duncan, Street, Julian, and 

 Micks (1959), and Meyer and Oliveira Musacchio (1960). Stages 

 in the mosquito host have been examined by Duncan, Eades, 

 Julian, and Micks (1960), Garnham, Bird, and Baker (1960), and 

 Garnham, Bird, Baker, and Bray (1961). The greater part of the 

 following account of vertebrate stages is drawn from the extensive, 

 high-resolution studies of Rudzinska and Trager. 



Several parasites may occur within a single host erythrocyte. 

 They are embedded in the red cell cytoplasm and surrounded by 

 two unit membranes, both of which are assumed to belong to the 

 parasite (Figs. 33 and 34, PL X). (Duncan and colleagues, 1959) 

 reported that some individuals were surrounded by three mem- 

 branes and suggested that these were gametocytes.) The cytoplasm 

 contains scattered or clustered Palade particles, variable amounts 

 of endoplasmic reticulum and some larger vacuoles. Smooth- 

 membraned sacs and vesicles identifiable as Golgi elements are 

 seen occasionally. Mitochondria are present in several species of 

 Plasmodium, but in P. berghei in rat blood (Rudzinska and Trager, 

 1959) none are evident. In this species elongate bodies composed 

 of two to six concentrically arranged double membranes (Fig. 34, 

 PL X) occur probably in all cells, and Rudzinska and Trager offer 

 the suggestion that these may be the sites of oxidative activity. 

 The membranes in some instances appeared to arise by invagina- 

 tion of both limiting layers of the cell surface. A second structure 

 of unknown significance, seen in the same species, is a sausage- 

 shaped vacuole with a double limiting membrane and structureless, 

 low-density contents. 



The most notable result of the studies by Rudzinska and Trager 



