RHIZOPODS, ACTINOPODS, SLIME MOLDS, SPOROZOA 95 



has been the discovery that cytoplasm of the host erythrocyte is 

 taken into the Plasmodium body in food vacuoles invaginated and 

 pinched off from the cell surface (Fig. 33, PI. X). Except for 

 minute bulges or wrinkles of the surface membranes, the contours 

 of the cell are smooth and even, with no suggestion of ameboid 

 activity ; hence this drawing-in of food is a rather novel form of 

 phagocytosis and suggests a membrane activity characteristic of 

 pinocytosis. Digestion of the ingested protoplasm, with con- 

 comitant accumulation of the residual pigment, hematin, occurs 

 either within the food vacuole as in P. lophurae in duck red cells, 

 or in subsidiary vacuoles budded off from it in P. berghei. Food 

 vacuoles frequently occur near the rather large nucleus and may 

 indent it deeply. The growing parasite eventually engulfs most 

 of the erythrocyte cytoplasm, and nuclear fissions begin. At this 

 stage, studied in P. lophurae, the endoplasmic reticulum is abundant 

 and mitochondria are numerous. Double membranes begin to 

 appear in the cytoplasm, outlining areas into which the cytoplasmic 

 organelles are segregated and which develop into individual 

 merozoites. The remainder of the mother cell, consisting mainly 

 of old food vacuoles and lipid droplets in a watery fluid, is left 

 behind as a residual body when the merozoites are completed. No 

 mitotic events were observed. 



Studying exoerythrocytic stages in the . chicken parasite, 

 P. gallinaceum, in infected tissue cultures, Meyer and Oliveira 

 Musacchio reported finding no mitochondria and no evidence of 

 food vacuole formation in feeding stages. The cytoplasm con- 

 tained many dense bodies that were not identifiable at the resolu- 

 tions achieved. Merozoite formation proceeded as described by 

 Rudzinska and Trager. Liberated merozoites often had a dense, 

 ring-like structure just beneath or in the cell membrane at one pole. 



This ring- or cup-shaped structure, about 120 m/x in diameter, 

 was also found at one pole of sporozoites of P. gallinaceum and of 

 P. falciparum by Garnham and colleagues (1960, 1961), who 

 studied them in the salivary glands of infected mosquitoes. In 

 addition these authors found a paired organelle consisting of two 

 dense, flattened, elongate (about 1 -4 /x) lobes narrowing at the 

 anterior end in proximity to the polar cup, and 12 or more tubular 

 fibrils about 19 mtt thick, arranged longitudinally at the periphery 



