2 7 8 



THE SPOROZOA 



Myxosporidian may exhibit a certain amount of differentiation at 



its outer surface to form a limiting 

 membrane or envelope. In the 

 second place, the parasite may be 

 spread over a considerable area of 

 the tissue infected, producing the 

 condition aptly termed by Thelohan 

 that of diffuse infiltration (Fig. 82). 

 In this case, the protoplasmic body of 

 the parasite and the cells of the tissue 

 are inextricably commingled, and as 

 the former is gradually used up to 

 form spores, a condition is finally 

 reached in which the tissue is found 

 to be infiltrated with vast numbers 

 of spores lying isolated from one 

 another, or in groups between the 

 cells. The concentrated condition of 

 the parasite is usually distinctly 

 visible to the naked eye, as little 



gpots j n th(J t i ssues . t h e diffuse COn- 



dition requires microscopic investi- 

 gation in order to discover the parasite. Some species occur 

 indifferently in either state, others only in one or the other 

 condition. 



FIG. Si. 



Transverse section of a stickleback 

 (Gasterosteus aculeatus), showing two 

 cysts of Glugea anomala, Moniez (KK), 

 in the body musculature on the right 

 (From Wasielewski, after Thelo- 



Associated with the parasites in the tissues there are frequently to 

 be found large numbers of "yellow bodies," the nature of which is 

 doubtful ; whether, that is to say, they are products of the parasite or of 

 the host. They are often very conspicuous, and often enclose spores (see 

 Doflein [100]). 



An interesting fact was brought to light by Hofer and Doflein with 

 respect to the destructive " Pockenkrankheit " of the carp. The disease 

 shows itself in the form of large indurated tumours of the skin, consisting 

 of epithelial growths which are invaded by leucocytes and by a prolifera- 

 tion of blood-vessels from the cutis. The most careful search failed, 

 however, to discover parasites or intruding organisms of any kind in 

 these tumours, but in all the diseased fish Myxobolus cyprini was found to 

 occur plentifully in the spleen, liver, and kidneys. Hence these authors 

 explain the skin-eruption of the carp as an indirect effect of the inter- 

 ference with the metabolism caused by the presence of the parasite in the 

 internal organs, more particularly in the kidney. This view has, however, 

 been sharply criticised, especially from the medical side (see Liihe [5], 

 pp. 85, 86). 



(c) Morphology. (1) The Trophic Stage. The trophozoite of the 

 Myxosporidia is remarkable, as has been said, for its amoeboid form 

 and Rhizopod-like appearance. In all but very young forms, the 



