26 



PROTOZOOLOGY 



enlarged parasites, undergo various morphological changes. For 

 example, 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 myxosporidian, Thelohanellus notatus, the connective 

 tissue cells of the host fish surrounding the protozoan body, trans- 



?^fl^^^S^SS!f:^^. 





ks^-yy--- 



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

 infection, X1920 (Kudo), a, portion of a cyst of Mijxoholus intestinalis, 

 surrounded 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. 



form themselves into "epithelial cells" (Fig. 1, 6), a state com- 

 parable to the formation of the ciliated epithelium from a layer 

 of fibroblasts lining a cyst formed around a piece of ovary in- 

 planted into the adductor muscle of Pecten as observed by 

 Drew (1911). 



Practically all Microsporidia are cytozoic, and the infected 

 cells become hypertrophied enormously, producing in one genus 

 the so-called Glugea cysts (Fig. 220). In many cases, the hyper- 

 trophy of the nucleus of the infected cell is far more conspicuous 

 than that of the cytoplasm (Fig. 218). Information concerning 



