THE MYXOSPORIDIA, OR PSOROSPERMS OF FISHES. la 
no affinity with the “ psorosperms,” it is none the less inevitable that, 
as between the generic definition and the type species, the generic name 
must follow the fate of the type species. 
Robin’s name Psorospermia can not, therefore, be employed as the sub- 
classic designation of, and for the same reason it can not be used as a 
generic name in, the Myxosporidia. 
In this connection it may be noted that the name Psorospermium has 
obtained currency in the Sporozoa. Apparently I have not found the 
original use of the name, and can only give the following references. 
The forms are nonmyxosporidian (see also p. 135)- 
Psorospermium, Paulicki, 1872, Mag. f. d. gesammt. Thierheilkde, Berlin, Xxxvin, 
p. 6; 7b., Rivolta, 1878, Giorn. Anat. Fisiol. e Patol., Pisa, x, p. 233. 
THE SUBCLASSIC DEFINITION.! 
Sporozoa, whose adult stage is characterized by the presence of num- 
erous nuclei originating by division; further by the power of amceboid 
movement,’ and by the mode of spore formation, which takes place 
in definite transparent areas (pansporobiasts), and which is progressive, 
not being confined to the last stage of the life cycle;* whose spores 
exhibit always 2 and sometimes 3 axes of symmetry and possess a shell 
resistant to chemical reagents, 1 or more capsules (each inelosing a 
coiled filament capable of extrusion), and a single mass of sporoplasm; 
type order Phenocystes. 
IlL— MORPHOLOGY. 
GENERAL DESCRIPTION OF STRUCTURE. 
Omitting discussion of controverted questions and of peculiarities 
correlated with generic differences, the life-history and morphology of 
the subclass may be briefly outlined as follows: 
In all the Myxosporidia two distinct stages are recognizable, viz, the 
myxosporidium (growth-reproduction or adult stage) and the spore. 
In addition a cyst may be present (see p. 77). 
1. The myxosporidium.—At the time of its exit from the spore the 
myxosporidium possesses nuclei and sometimes a vacuole. It. now‘ 
1Original. The first Gefinition of the group was given by Lankester, as follows: 
“‘Sporozoa, in which the euglena-phase is a large multinucleate amceba-like 
organism. The cysts are imperfectly known, but appear to be simple. Some attain 
a diameter of two lines. The spores are highly characteristic, having each a thick 
coat which is usually provided with a bifurcate process or may have thread capsules 
(like nematocysts) in its substance. The spores contain a single nucleus and are not 
known to produce falciform young, but in one case have been seen to liberate an 
amebula. The further development is unknown. The Myzxosporidia are parasitic 
beneath the epidermis of the gills and fins, and in the gall bladder and urinary bladder 
of fishes, both fresh-water and marine.” 
?Except possibly Thelohania, in which the myxosporidium is unknown. 
5 Noted by Biitschli (Bronn’s Thier-Reich, 1882, 1, p. 595) in Myxobolus miilleri and 
Myxidiwm lieberkiihnii. 
4 Fide Pfeiffer; cf. Korotneff ; see pp. 187, 288, pl. 9, fig. 1, and pl. 46, fig. 1b. 
