78 EEPORT OF THE COMMISSIONER OF FISH AND FISHERIES. 



composed of clear, very finely granular protoplasm, containing many 

 small nuclei which i)ossess a distinct dark membrane and a somewhat 

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

 to determine certainly whether this membrane is formed by the myxo- 

 si)oridium 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 endoplasm. 

 Balbiani's^ views of cyst structure may be summed up thus: 

 Membrane of rather firm texture, very thick (sometimes 10 /<) without structure, 

 showing small refringeut granulations. 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 production of the parasite rather than of 

 the host. 



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

 the host. 



Thelohan^ could find 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 nonnucleated) myxosporidian ecto- 

 plasm. Finally, he says, CystocUscus immersus (which is free-floating) 

 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 mugilis a 

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

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

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

 that in certain other forms, especially Gystodiscus inimerstis^ which is 

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

 membrane is a product of the myxosporidium. Still other species (e. g., 

 Myxidium Ueherlcalmii) 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 ectoplasm of the myxosporidium and the 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 Th61ohan^ 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 



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

 sjahresber. d. rhein. Fisch.-Vereins Bonn^ 1888, p. 31. 

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

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

 «BuU. Soc. philomat. Paris, 1892, iv, pp. 168, 169. 



