112 REPORT OF THE COMMISSIONER OF FISH AND. FISHERIES. 
V.—CLASSIFICATION OF THE MYXOSPO 
Although several times previously authors had proposed generic 
names (apparently 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 Thélohan.? The following is Thélohan’s 
primary classification : 
Mysxosporidians. 
Pyriform; capsule 1, at pointed extremity; vacuole 1, } 
aniodinophile, at large extremity. 
|e vacuole; capsules 
Spores .. 4 2 or 4. 
Capsules 2.- 
ees variable.... 
The 3 principles laid down by him as a basis for classification may 
be thus summarized: 
RIDIA.! 
I. Glugeidians. 
Il. Myxidians. 
Capsules 4.. III. Chloremyzans. 
Vacuole1, iodinophile. Capsules 1-2. IV. Myxobolans. 
1. The habitat furnishes no sound basis for specific distinctions. 
Here the following judicious criticism by Thélohan 
Beyond the difference of their habitat, Perugia mentions no other characters 
may be quoted: 
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 myxosporidian 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 the 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 
1The classification given below has already been published as a preliminary note 
in the Bulletin of the Commission for 1891 (x1, pp. 408-412). 
sion contains everything there given with some amplifications. 
2 Bull. Soc. philomat. Paris, 1892, 1v, pp. 165-178, 
The present discus- 
