220] 



The Classification of Lower Organisms 



Order Cnidosporidia Doflein Protozoen 177 (1901). 

 Order Myxosporidia Calkins Biol. Prot. 449 (1926). 

 Most species of this order parasitize fishes, living either in internal cavities or in 

 the tissue cells; fewer than a dozen species are known from miscellaneous other ani- 

 mals, amphibia, reptiles, insects, and worms. Most of these parasites are not 

 extremely injurious. 



The infective protoplast which issues from a spore is, at least usually, binucleate. 

 The nuclei fuse and the fusion nucleus divides repeatedly as the plasmodium grows. 



Fig. 43.— Diagram of the life cycle of Myxoceros Blennius after E. Noble (1941). 



In the examples which are believed to be more primitive, the plasmodia are freely 

 capable of budding, and the mature plasmodia are rather small and are converted as 

 wholes into single or paired spores. In the remaining examples, the plasmodia do not 

 multiply by budding, but produce spores continually. 



Noble (1941) described the mitotic process. There is a rather large intranuclear 

 centrosome, which divides, the daughter centrosomes moving to opposite sides of 

 the nuclear cavity. Four chromosomes appear; this is apparently constant throughout 

 the order. The nuclear membrane and the centrosomes disappear. No spindle has 

 been seen. The chromosomes divide, and the daughter chromosomes move apart and 

 melt into two masses. The masses swell, a nuclear membrane appears about each, 

 and a centrosome appears inside of each. 



