112 REPORT OF THE COMMISSIONER OF FISH AND FISHERIES. 



v.— CLASSIFICATION OF THE MYXOSPORIDIA.i 



Although several times previously authors had proposed generic 

 names (aj^pareutly merely because the forms looked quite different, and, 

 if we may judge from the absence of even a single generic definition to 

 support any of the generic names, probably without any clear idea of 

 the direction of generic lines) the first serious attempt at classification 

 of the subclass was made by Thelohan.^ The following is Thelohan's 

 primary classification : 



Myxosporidians. 



The 3 principles laid down by him as a basis for classification may 

 be thus summarized: 



1. The habitat furnishes no sound basis for specific distinctions. 

 Here the following judicious criticism by Thelohan may be quoted: 

 Beyond the difference of their habitat, Perugia mentions uo other characters 



which enable him to distinguish specifically the organisms that he has observed. 

 But the habitat can not serve as a criterion, for, in addition to its being a fact entirely 

 removed from the morphologic, histologic, and developmental characters of the 

 parasite, it frequently happens that the same form lives at the expense of very dif- 

 ferent hosts, and, besides, a myxosporidiau habitually parasitic ou one iiarticular 

 host can accidentally invade a different species. 



The conditions under which the parasite is encountered can not better be taken 

 as a distinctive character, for tlie same species can present itself under very differ- 

 ent states; for example, under the form of small, well-circumscribed tumors, or an 

 irregular infiltration of the tissues. 



There is little to add to this, except the hope that it may succeed in 

 directing future investigations toward the parasite rather than the 

 host. 



2. The myxosporidium affords no taxonomic criteria. 



The myxosporidium exhibits characters that are too nearly identical and too little 

 contrasted to serve as bases for specific determinations. It is, however, possible 

 and advantageous to take account of it, especially in the forms living free in the 

 internal cavities, in which forms its differentiations are much more marked. 



3. The spores alone (at least in the present state of our knowledge) 

 offer characters suitable to serve as a basis for classification. 



By noting the differences of form and size of these elements, the number of their 



• The classification given below has already been published as a preliminary note 

 in the Bulletin of the Commission for 1891 (xi, pp. 408-412). The present discus- 

 sion contains everything there given with some amplifications, 



2 Bull. Soc. philomat. Paris, 1892, iv, pp. 165-178. 



