78 REPORT OP THE COMMISSIONER OF FISH AND FISHERIES. 



coini)osed of clear, vciy fiilely granular protoplasm, containing- many 

 small nuclei which possess a distinct dark m(Miil)rane and a somewhat 

 irregular outline, and stain intensely with alum carmine. It is difficult 

 t;0 determine certainly whetlier this membrane is formed hy the myxo- 

 sporidium or by the host. Opposing the myxosporidian origin (which, 

 however, is in no wise excluded) is the relatively greater size of the 

 membrane nuclei compared with those of the endoi)]asm. 

 ]>albiani's' views of cyst structure may be summed up thus: 



Meiiibrjine of rather firm texture, very thick (sometimes 10 /i) witliout structure, 

 showing small refringent granubitions. In spite of Biitschli's assertion of the 

 presence of carmine-staining nuclei, Balbiani could find nothing definite. He is 

 disposed to regard the membrane as a jiroduction of the parasite rather than of 

 the host. 



Ludwig^ believes the cyst membrane to be probably a production of 

 the host. 



Thelohair' could fiiul no nuclei in the cyst membrane and believes 

 their absence an argument of real value in favor of the derivation of 

 the membrane from the (similarly non nucleated) myxosporidian ecto- 

 plasm. Finally, he says, Cyntodiscus immersus (which is free-lioating) 

 is surrounded by a clearly defined structureless membrane. 



Perugia'' has, it seems to me, recently made an important contribu- 

 tion to this subject. This observer has seen in Myxobolus mmjilis a 

 cyst which contained three separate myxosporidia. (See p. 213, pi. 14, 

 fig. 5.) It is hard to resist tlie conclusion tliat, in this case at least, the 

 host furnished the cyst membrane. But it is equally dillicult to deny 

 that in certain other forms, especially Cystodiscus immersus, which is 

 free-floating in the bile, (1) that there is a membrane and (2) that such 

 membrane is a product ol" the niyxosporidium. Still other species (e. g., 

 Myxidlum lieherlcillmii) show an ectoplasmic membrane. I suspect the 

 explanation to be that the "cyst membrane" is really composed of two 

 concentric membranes, one (the inner and constant one, whose degree 

 of development and of condensation, however, probably varies greatly) 

 being the ectojdasm of themyxosporidium andthe other (the outer and 

 inconstant one, being absent, for example, in the free-floating forms) 

 being a product of the tissues of the host. 



Finally Th6Iohan^ has recently put forth essentially the same view, 

 viz, that the so-called cyst membrane is not derived from but is merely 

 the ectoplasm of the myxosporidium modified. His observations are 

 as follows : 



Those Myxosporidia which form well-defined cysts {e. g., the branchi- 

 colous species) have the ectoplasm still distinct, but no pseudopodia 

 are seen. Formerly he admitted the existence of a cyst membrane 



' Journ. de Microgr., 1883, vii, pp. 199, 200. 



* Jahresber. d. rhein. Fisch.-Vereins Bonn, 1888, p. 31. 



» Annal. de Microgr., 1890, ii, pp. 203-205. 



<Boll. Scientif., Pavia, 1891, xiii, pp. 23, 24. 



6 Bull. Soc. philomat. Paris, 1892, ix, pp. 168, 1G9. 



