THE MYXOSPORIUIA, OR PSOROSPERMS OF FISHES. 89 



Eemarls. — Balbiani, Tlicloliaii, and Mingazzini appear to assume, as 

 the basis for their criticism of Prof. Biitschli's view, that a structure 

 morphologically a iiematocyst 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. 



Concerjiing the homologies of the organs in question it is impossible 

 to see how, as suggested by Mingazzini, they are to be brought into 

 comiiarison 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, etc. 



I can not, however, feel much greater confidence in their homology 

 with the coelenterate 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 coelenterate nematocyst, it j)resents one 

 very important difference, viz, that it ajipears and functions at an en- 

 tirely difierent 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. Th61ohan (p. 87), and their (probable) utter uselessuess 

 to the myxosporidian spore as offensive or defensive weapons, and the 

 parallel is 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 i)roducing 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, 



iLankester, E. Ray, 1878, Encycl. Britan., 9 ed., vi, p. 108. 



