THE MYXOSPORIDIA, OR PSOROSPERMS OF FISHES. 73 



no affinity with the "psorosperms," it is none the less inevitable that, 

 as between the generic definition and the type sj^ecies, the generic name 

 must follow the fate of the tyj)e species. 



i^obin's uame 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 Mijxosporidia. 



In this connection it may be noted that the name Fsorospermiumhas 

 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 noumyxosporidian (see also p. 135)- 



Psorospermium, Paulicki, 1872, Mag. f. d. gesammt. Thierlieilkde, Berlin, xxxviii, 

 p. 6j i6.,Rivolta, 1878, Giorn. Auat. Fisiol. e Patol., Pisa, x, p. 233. 



THE SUBCLASSIC DEFINITION.! 



S2)orozoa, whofie adult stage is characterized by the presence of num- 

 erous nuclei originating by division; further by the power of amoiboid 

 movement,^ and by the mode of spore formation, which takes place 

 in definite transparent areas (pansporoblasts), 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 inclosing a 

 coiled filament capable of extrusion), and a single mass of sporoplasm; 

 type order Fhwnocystes. 



II.— 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 My.rosporUUa 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* 



'Original. The first definition of the group was given by Lankester, as follows: 

 " Sporozoa, in which the englena-phase is a large multinucleate amopba-like 

 organism. The cysts are imperfectly known, but ajipear 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 

 amoibula. The further development is unknown. The Myxosporidia 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." 



2 Except possibly Tlielohania, in which the myxosporidium is unknown. 



3 Noted by Biitschli (Bronn's Thior-Reich, 1882, i, p. 595) in Myxobolus mUlleri and 

 Myxidium lieberkUh n ii. 



*Fide Pfeiffer; cf. Korotueff ; sec pp. 187, 238, pi. 9, fig. 1, and pi. 16, fig. lb. 



