THE MYXOSPORIDIA, OR PSOROSPERMS OF FISHES. TD 
DETAILED DESCRIPTION OF INDIVIDUAL STRUCTURES. 
‘PSOROSPERMS” THE SPORES. 
The older writers seem to have tacitly admitted that their “psoro- 
sperms” represented the spore stage. Thus Lieberkiihn! says that cer- 
tain animals fix themselves to the skin of fishes and in reproduction fall 
apart into the “psorosperms.” Balbiani,? however, regarded the ‘‘ pso- 
rosperms” as an adult eryptogam. This view he subsequently virtually 
abandoned.® All the later authors, without exception, have regarded 
the myxosporidium as the adult. 
THE MYXOSPORIDIUM.. 
This was first observed by Dujardin in 1845 (see p. 273). It occurs 
free or attached. Size 2 mm. or, more usually, much less, without 
constant or characteristic body-form, being cylindrical, ribbon- , or 
club-shaped, or more or less globular or irregularly ameeboid, consisting 
of colorless or more or less yellowish protoplasm (pigment usually 
extraneous, see p. 76); usually, probably always, showing a more or less 
(frequently quite) distinct differentiation into ectoplasm and endoplasm. 
In the cyst-forming Myxosporidia (e. g., the branchicolous forms) the 
differentiation is also, at least in the older myxosporidia, very sharp. 
ECTOPLASM. 
Forming a very transparent granule-free or exceedingly finely 
granular zone, from which all of the elements characteristic of the 
endoplasm are absent. 
1 Miiller’s Archiv., 1854, p. 357. 
2 Compt. Rend. Acad. Sci. Paris, 1863, Lv, p. 159. 
3 Journ. de Microgr., 1883, vil, pp. 198, 201, 276. 
4 Pfeiffer regards the large myxosporidia as composed by the fusion of many small 
ones. He thus explains progressive spore formation: 
“With the view here expressed that the smallest psorosperm-tubes of the barbel 
are simple myxosporidia (‘sporoblasts’) similar to those of Himeria in the schematic 
table, and to those of the Microsporidia; further, that the large tubes are a con- 
glomerate of many different individual parasites which have run together accident- 
ally in Gregarine fashion, and that their cyst nature originates through cicatricial 
incapsuling by the host, some things apparently do not entirely agree. Why are the 
large tubes empty in the middle? Where have the contents gone? ‘They can not be 
a consumed residual mass.) How are to be explained the appearances simulating 
nuclear division on the capsule wall in figs. 9 and 14? Does this last-mentioned . 
fact compel us to admit after all a progressive endogenous division and a successive 
infection? We have above answered this in the negative; they must admit of 
definite solution when more comparative investigations (e. g., upon batrachians 
and birds) shall be at hand.” 
Subsequently (see p. 227) he explains the emptiness of the central portion by a 
supposition of spore-migration towards the periphery in search of better nutritive 
conditions. 
A similar pressure-fusion occurs in ‘“Myxosporidium” bryozoides (p. 188). 
