THE MYXOSPORIDIA, OR PSOROSPERMS OF FISHES. 89 
Remarks.—Balbiani, Thélohan, and Mingazzini appear to assume, as 
the basis for their criticism of Prof. Biitschli’s view, that a structure 
morphologically a nematocyst must necessarily be urticant in function, 
in other words that the terms nematocyst and urticant organ are 
synonymous. This assumption is, to say the least, very dubious. 
Concerning the homologies of the organs in question it is impossible 
to see how, as suggested by Mingazzini, they are to be brought into 
comparison with the falciform bodies of the gregarine and coccidian 
spores, inasmuch as (as noted by Schneider; see p. 85) the falciform 
bodies are not in any respects structurally similar to the myxospori- 
dian capsules, and further it would seem (as implied in Leuckart’s view 
above given) that the homology should lie between the protoplasmic 
structure in the one spore, and the protoplasmic structure in the other, 
whereas Mingazzini’s parallel is between the protoplasm in the one and 
a structure which shows no evidence of such composition in the other, 
being apparently destitute of such characteristic protoplasmic struct- 
ures aS nuclei, vacuole, ete. 
I can not, however, feel much greater confidence in their homology 
with the celenterate nematocyst. I can only interpret homology to 
mean such correspondence in development and structure as would (upon 
the evolution theory) imply descent from a common ancestor, and con- 
versely no homology seems possible except in cases where (upon the 
same theory) one would be willing to admit such common origin. 
In the present case, while the myxosporidian capsule shows a marked 
histologic resemblance to the ccelenterate nematocyst, it presents one 
very important difference, viz, that it appears and functions at an en- 
tirely different period of the life-history, i. e., it characterizes the spore 
and disappears before the adult stage is reached. Add to this the 
point cited by M. Thélohan (p. 87), and their (probable) utter uselessness 
to the myxosporidian spore as offensive or defensive weapons, and the 
parallelis by no means close enough to justify their assimilation to the 
nematocysts. The fact that the myxosporidian filament agrees (how 
closely ?) with that of Hydra in having the filament first extruded and 
only subsequently retracted-coiled, does not seem sufficient to prove 
the morphological equivalence of the structures, as it might be possible 
that this mode of formation is the only one capable of producing the 
necessary elastic tension. Further,’ “nematocysts” are known in 
some mollusks. All these facts render it very probable that these 
‘““nematocysts” have been independently evolved in the different 
groups. It may, however, well be a question to what extent of detail 
all of these “nematocysts” correspond. 
As regards the function of the capsules and filaments, the only intel- 
ligible suggestion that has yet been made appears to be the view of 
Leuckart and Biitschli, which sees in them an apparatus for attach- 
ment. I can see no basis in the facts for Balbiani’s antherozoid theory, 
1Lankester, E. Ray, 1878, Encycl. Britan., 9 ed., v1, p. 108. 
