112 REPORT OF THE COMMISSIONER OF FISH AND FISHERIES, 

 v.— CLASSIFICATION OF THE MYXOSPORIDIA.' 



Although several times previously authors had proposed generic 

 names (apparently merely because the forms looked (piite different, and, 

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

 supi)()rt any of the generic names, i)robably without any clear idea of 

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

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

 primary classification : 



Mi/xosporidiatis. 



Pyrit'onn: caiisiile 1, at pointed extremity ; vacuole 1, ? I. (.Ilwjcidians. 

 "aiiiodiiiDpliile, at large extremity. > 



( f Capsules 'J.. 11. Mi/xidiann. 



Ko vacuole ; capsules J 



I'orm vanablo.... , | Capsules 4.. III. (Udurumijxans. 



, Vacuolol, iodinopliile. Capsules 1-2. IV. Myxobolans. 



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

 be thus summarized : 



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

 Here the following judicious criticism byThelohan maybe quoted: 



licyoud the difference of their liabitat, Perugia mentions no other characters 

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

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

 removed from the mori>hologic, histologic, and developmental characters of the 

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

 ferent hosts, and, besides, a myxosporidiau habitually parasitic on one particular 

 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 infiltratlou 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 myxosi)oridium affords no taxonomic criteria. 



The myxosporidium exhibits cliaracters that ai(f too nearly identical and too little 

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

 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 i)rcsent 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 tlie Bulletin of the Comunssion for 1891 (xi, pp. 108-112). Tfie present di.scua- 

 sion contains everything tiiere given with some amplifications. 



»Bull. Soc. philomat. I'aris, 18i»2, iv, pp. 165-178. 



