MYXOSPORIDIA. 



65 



iii the tissues. The tissue-forms occur either in cysts, which are 

 often visible to the naked eye, or in an infiltrated form, and they 

 may infest almost any tissue (bone, cartilage excepted). 



It is not quite clear to 

 what extent they are cell- 

 parasites. Many of them 

 are certainly intracellular 

 in the young state, and it 

 is possible that all may be 

 so ; but the youngest stages 

 have not been studied in 

 all forms. Sporulation in 

 the intracellular forms may 

 begin in the quite young 

 forms, even before they 

 have outgrown their cell- 

 host. The Myxosporidia 

 differ from other Sporozoa 

 in their tendency to cause 

 tumours in their host. 

 They may cause serious 

 diseases : the silk - worm 

 disease has been referred 

 to, and they have been 

 known to cause serious 

 mortality among fishes. 



Those which lead a free 

 life are amoeboid and vary 

 much in shape (Fig. 54). 

 The shape of the cysts and 

 of the infiltration -forms 

 depends upon the physical 

 condition of the tissues. 



The Myxosporidia, though amoeboid, do not take up solid food, 

 but resemble other Sporozoa in absorbing the nutritive juices of 

 their hosts. The body shows a division into ecto- and endoplasm. 

 The nuclei are numerous and lie in the endoplasm, which contains 

 granules and fat-drops. 



Reproduction takes place by spore-formation. They differ, however, from 

 other Sporozoa in the fact that the whole body does not break up into spores at 

 one time, but the spores are formed gradually in the endoplasm while the parent 



F 



FIG. 54. Leptothcca agilis as a type 01 free-living Myxo 

 sporidia, from the gall-bladder of Trygon vidgaris- 

 ps pseudopodia ; g fat-drops ; ; refractile granules ; 

 sp spores (after Thelohan). 



