THE MYXOSPORIDIA, OR PSOROSPERMS OF FISHES. 75 



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 reprodnction fall 

 apart into the "psorosperms." Balbiani,'^ however, regarded the "pso- 

 rosperms" as an adult cryptogam. 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 anueboid, 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 sharj). 



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, lvii, p. 159. 

 * Jonrn. de Microsr., 1883, vii, pp. 198, 201, 276. 



■♦ 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 Eimeria 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? Wliero 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 tigs. 9 and 14? Does this last-mentioued 

 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 batrachiana 

 and birds) shall be at hand." 



Subsequently (see p. 227) he explains tb.e 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). 



