MYXOBOLID^E 31 



nuclei and, occasionally, also the homogeneous reproductive body into 

 which they fuse. The nematocysts also become visible with the 

 remains of the two nematocystic nuclei still clinging to them. A 

 rough idea of the general structure of the cnidospores and nematocysts 

 may be gained by fixing whole Myxosporides and clearing them in 

 glycerine. When required for use, they may be teased out in the same 

 fluid and embedded in glycerine jelly. As in the case of Nematodes 

 and the eggs of Helminthes, Myxosporides should be fixed in 70 per 

 cent, hot alcohol to which 5 per cent, glycerine is added, the alcohol 

 being allowed slowly to evaporate. 



The best method of examining the whole organism is by means of 

 sections cut from the infected gill lamella, which should be fixed 

 whole in alcoholic solution of mercuric chloride. It will then become 

 apparent that the parasite is surrounded by an envelope derived from 

 the tissues of its host. The ectoplasm is somewhat thickened, but a 

 true cyst, forming an integral part of the parasite itself, has not been 

 observed. The interior of the parasite is entirely filled with cnido- 

 spores in all stages of development, which are separated from one 

 another by scanty remnants of endoplasm. The development of the 

 cnidospores is similar to that of Sphceromyxa, but it is more difficult 

 of observation. Certain forms, however, may be recognized with 

 comparative ease. These are : single nuclei, round which a portion 

 of plasma has collected and which were formerly believed to be pan- 

 sporoblasts ; the developmental stages of pansporoblasts containing 

 several nuclei ; and the final stages of spore formation. 



It is now very generally recognized that the spores are not formed, 

 in the first instance, from a plasmic body containing a single nucleus. 

 It is probable that, in the initial stage, two nuclei, round which a 

 portion of plasm has collected, come together to form the pansporo- 

 blast, without fusion of either nucleus or plasm (Mercier, Keysselitz 1 ). 

 Thus the pansporoblast is originally two-celled, and nuclear division 

 does not cease (as was formerly believed to be the case) when eight to 

 ten daughter-nuclei are formed, but continues until these are fourteen 

 (characteristic of the order) in number, their further development 

 resembling that of Sphceromyxa (fig. 5). 



Myxobolides do not only occur upon the gills ; all the organs, with 

 exception of the skeleton, may be affected. The following species 

 have a practical importance : 



(1) Henneguya oviperda (Cohn). Parasitic in the eggs of the 

 pike, which, when affected, appear white in colour. They are very 



(1) See Braun, " Parasitenlehrbuch," 4th ed., p. 135; also G. Keysselitz, " Die 

 Entwickelung von Myxobolus pfeifferi, Th.," part i, Arch. f. Protistenkunde, vol. ii, 

 1908, pp. 252-275. 



