722 OEDER: MYXOSPORIDIIDA 



the binucleate stage is not produced by union of two uninucleate indi- 

 viduals, but by the actual division of the nucleus of the uninucleate form. 



The order Myxosporidiida is divided by Doflein (1901) into two sub- 

 orders, Disporea and Polysporea. The members of the former are 

 parasitic in the body spaces as large amoeboid organisms, which may 

 measure as much as 85 by 25 microns. Within each individual a single 

 cell (pansporoblast) is separated in a vacuole. The single uninucleate cell 

 by further development gives rise to two spores, which remain embedded 

 in the cytoplasm of the adult. After their formation the parasite dies 

 and the two spores are liberated. In the Polysporea, which include the 

 majority of the Myxosporidiida, the adult parasite produces a large number 

 of spores. It is these forms which invade the tissues, give rise to large 

 tumours, and often produce an intense infection of the host. In an 

 infected area of tissue, which can only be satisfactorily examined in 

 sections, it is frequently difficult to define the limits of a single parasite, 

 which extends as a reticulum amongst the tissue cells and fibres, producing 

 the condition known as difiuse infiltration (Fig, 306). In such cases the 

 spores, when produced, are scattered amongst the tissue elements, which 

 often show marked hypertrophic changes, though sometimes this does not 

 occur, the individual cells and fibres being little altered in appearance. 

 In those cases in which a fibrous capsule is formed, the multinucleate 

 layer of cytoplasm which lines the capsule appears to be a single parasite. 



Kudo (1919) has, however, pointed out that such a division into 

 Disporea and Polysporea is an artificial one, as the number of spores 

 produced by any particular species is by no means as constant as such a 

 classification implies. He maintains that the spore stage is still the only 

 one which affords constant characters by which various genera and 

 species can be identified (Fig. 307). 



The spore consists of a shell composed of two valves which are united 

 in a sutural plane like two watch-glasses placed with their rims together. 

 The sutural line may be straight, as in the case of watch-glasses, or it may 

 be more irregularly curved, giving the appearance of an S in side view. 

 The form of the spore varies with the shape of the valves and the presence 



1. Leptothera informis. 13. Sinuolinea capsularis. 



2. Myxnimili iisrnrnutiis. 14. Mi/.n'di/nit /inirenwi: 



3. Wanlni ,>rn,nn,a. IT). M i/xld, ma i ii llatum. 



4. Ceni/niiif/.iii sjiinosa. 1<>. Splm rnnn/ni Im'hiami. 



5. Ccniluiin/ni Iriiiiral/l. 17. S plui rniini.ni I iir ii mild. 



6. Ccnihnn'ii.nt nnirrahi.. IS. Z.-^rlmkl.; Iht a,h, lln,, imilii . 



7. Crr,tln„iiix<i sphrrK/om. li). J/y.ro.v„/,„/ ,l,iianli„l. 



8. J////v^^•/-u/v/ riiprlni. 2(1. .\h/.n,su„m dnjanlini. 



9. Mllnispuni niiidata. 21. f.rj,ln.<i„,ni nnila. 



10. Ch!on>,u//.nnn. leydigi. 22. Mi/.ruh,diis nmissii. 



11. Ghloromyximh caudatum. 23. Hoferdlus cyprini. 



12. Sphcerospora rostraia. 24. Henneguya gurleyi. 



25. Henneguya psorospennica. 



