222 IIEPORT OF THE COMMISSIONER OF FISH AND FISHERIES. 



urinary bladder of Lucius hiciuSj consisting of small free masses linii^g 

 the internal surface of the organ, the second consisting- of drawn-out, 

 chain-like masses in the midst of the tissues of the organ. The second 

 he believes to be merely a more advanced stage of the lirst. When the 

 parasite is only sligntly developed its presence is recognizable only bj^ 

 small opaque streaks in the otherwise transi)arcnt bladder, on opening 

 which the myxosporidium is found upon its internal surface. In other 

 cases snmll white prominences are found, presenting a transition between 

 the large mammillated masses described by Balbiani, and which can 

 attain 10 mm. in thickness. Sections showthe myxosporidium intimately 

 united to the epithelium. Tlie latter soon becomes broken up and the 

 plasmic chains insinuate themselves between the fibers of the connec- 

 tive tissue. 



By serial sections one can follow progressively the march of the para- 

 site into the tissues. Tliese last allow of separation and stretching of 

 the fasciae, such change being progressive and slow. Soon, however, 

 under the continuous pressure produced by the growth of the invading 

 mass, the fibers arrive at the limit of extensibility and finally rujiture. 

 Thus are formed irregular spaces, iu the middle of which oue finds the 

 debris of the tissue of the organ, surrounded by the rayxosporidia. 

 During this time spores are formed. They finally almost entirely 

 replace the protoplasm. In other parts of the same mass earlier and 

 intcrn.iediate stages can be seen. In the air bladder, as in the kidney, 

 the distinction between the ectoplasm and endoplasm is little evident 

 and, beyond the fact of the absence of nuclei from the ectoplasm, it is 

 ditticult to find characters to sei)arate these layers. 



{h) Of the external surface, Balbiani ^ gives, as the results of his 

 investigations, the following account of the development: ' 



Of all freshwater fishes the tench is most frequently affected with Myxosporidia 

 and at all seasons. This, together with the transparency of the fins of the young, 

 renders it especially favorable for investigation. Balbiani frequently observed 

 upon the fins, mingled with developed psorosperms, small amoeboid bodies of very 

 variable size. These move like the most agile amccbis (e. g., A. diffliicns), 9 changes 

 of form occurring in less than 15 minutes; temperature had great influence, heat 

 accelerating, cold retarding. The pscudopodia were large and obtuse, the mass 

 appearing lobed. as in A. diffluens. Unless obscured by fat globiiles (numerous in 

 the later stages), the nucleus is plainly visible, particularly at the time of the exit 

 of the mass from the spore. It is the nucleus of which Biitschli has proven the 

 existence in the interior of the psorosperm (cf. p. 208). There is no contractile 

 vacuole, and from this point of view these bodies differ from the ordinarj^'aracEba). 



While thus wandering over the fins, the small amcoboid bodies absorb nutriment, 

 grow, show more or fewer fatty globules, tend to take a rounded oval, or somt-times 

 irregular form with expansions and lobes, and tor surround themselves with a thin 

 envelope easily visible in water. As the water penetrates the fin tissue, the amoeboid 

 movements become more and more slow and finally cease. Independently of its 

 thin proper uuinibrane, the small mass is encysted in the same manner as other 

 foreign bodies, by the conuective tissue of the host. 



1 Journ. de Microgr., 1883, VU, pp. 272-4. 



