78 REPORT OF THE COMMISSIONER OF FISH AND FISHERIES. 
composed of clear, very finely granular protoplasm, containing many 
small nuclei which possess 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- 
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 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 refringent 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. 
Thélohan® 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, Cystodiscus 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 myxosporidia. (See p. 213, pl. 14, 
fig.5.) It is hard to resist the conclusion that, in this case at least, the 
host furnished the cyst membrane. But itis equally difficult 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 of the myxosporidium. Still other species (e. g., 
Myzxidium lieberkiihnii) 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 Thélohan® has recently put forth essentially the same view, 
viz, that the so-called cyst membrane is not derived from but 7s 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, vir, pp. 199, 200. 
2 Jahresber. d. rhein. Fisch.-Vereins Bonn, 1888, p. 31. 
3 Annal. de Microgr., 1890, 11, pp. 203-205. 
4Boll. Scientif., Pavia, 1891, xm, pp. 23, 24. 
5 Bull. Soc. philomat. Paris, 1892, rv, pp. 168, 169. 
