ECOLOGY 



27 



sugar. Malarial infection is invariably accompanied by an enormous 

 enlargement of the spleen ("spleen index"); the blood becomes 

 watery; the erythrocytes decrease in number; the leucocytes, sub- 

 normal; but mononuclear cells increase in number; pigment granules 

 which are set free in the blood plasma at the time of merozoite- 

 liberation are engulfed by leucocytes; and enlarged spleen contains 

 large amount of pigments which are lodged in leucocytes and endo- 

 thelial cells. In Plasmodium falciparum, the blood capillaries of 

 brain, spleen and other viscera may completely be blocked by in- 

 fected erythrocytes. 





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Fig. 1. Histological changes in host fish caused by myxosporidian in- 

 fection, X1920 (Kudo), a, portion of a cyst of Myxobolus intestinalis, sur- 

 rounded by peri-intestinal muscle of the black crappie; b, part of a cyst 

 of Thelohanellus notatus, enveloped by the connective tissue of the blunt- 

 nosed minnow. 



In Myxosporidia which are either histozoic or coelozoic parasites 

 of fishes, the tissue cells that are in direct contact with highly en- 

 larging parasites, undergo various morphological changes. For exam- 

 ple, the circular muscle fibers of the small intestine of Pomoxis 

 sparoides, which surround Myxobolus intestinalis, a myxosporidian, 

 become modified a great deal and turn about 90° from the original 

 direction, due undoubtedly to the stimulation exercised by the 

 myxosporidian parasite (Fig. 1, a). In the case of another myxo- 

 sporidian, Thelohanellus notatus, the connective tissue cells of the 

 host fish surrounding the protozoan body, transform themselves into 



