MYXOBOLID^: 29 



divide until there are fourteen nuclei in all, eight of which are usually 

 grouped in a peripheral circle round the other six (fig. 4, a). During 

 the next stage the pansporoblast divides into halves (sporoblasts) f 

 each of which contains six nuclei, while the remaining two nuclei,, 

 which from the beginning have been noticeable for their slightly 

 smaller size, are extruded as abortive and perish (fig. 4, 6). The 

 six-nucleated sporoblasts now release the cnidospores and, in this 

 manoeuvre, two nuclei, which are not visible in the ripe spore, are 

 utilized to form the two valves of the shell. TW T O other nuclei play 

 a part in the formation of the two nematocysts, which, as in the 

 Myxides, are placed at each end of the sickle-shaped cnidospores, and 

 to which, even in the adult spore, remains of the old nuclei may be 



FIG. 4. Formation of the cnidospores of Sphcsromyxa labrazesi (after Schroder). 

 a, Pansporoblast after completion of nuclear division ; the old nuclei, which are to be 

 extruded, are recognizable by their smaller size, b, Pansporoblast after division into two 

 sporoblasts ; rejection of the two old nuclei, c, Pansporoblast with young cnidospores, 

 showing the cells and nematocysts in process of formation, d, Finished cnidospore. e, A 

 nematocyst. (a to d magnified 1,200 : 1 ; e about 2,500 : 1.) 



seen adhering. The two central nuclei form the nuclei of the 

 amoeboid germ of sporoplasm (fig. 4, c and d). These two nuclei 

 of the sporoplasm (each of which is probably derived from one of 

 two other nuclei which combined to form the pansporoblast) finally 

 refuse to form a single nucleus. 



(c) MyxobolidcB. 



Small protuberances are frequently seen on the gills of fresh- 

 water fish. They are either round or oval in shape and, owing to 

 their white colour, they are easy of detection. They are the so- 

 called "cysts" of Myxosporidian origin, and belong to the family 

 Myxobolides. 



The milky contents of these cysts should be examined in the 

 fresh state. It consists almost entirely of cnidospores furnished with 

 two nematocysts, which are placed together at what is usually 

 termed the "front" pole. Two Myxobolides are recognized; they 



