THE NEOSPORIDIA 407 



According to Awerinzew (760), in Myxidium sp. a propagative cell may 

 give rise sometimes to a single spore, as in Cer atomy yea, in other cases to three 

 spores ; this must doubtless be interpreted to mean that a propagative 

 cell may become a sporoblast without entering into association with another 

 propagative cell, and that in other cases three propagative cells may form 

 an association ; these variations present an analogy with the solitary encyst- 

 ment or triple associations of gregarines (p. 331). 



The process of syngamy in these parasites has been described as being a 

 process of autogamy, but whether it is so or not depends entirely upon the 

 manner in which the plasmodium arises ; if a single, uninucleate amcebula 

 becomes a plasmodium by growth accompanied by nuclear multiplication, 

 then the sexual process is a case of autogamy ; but if, as is more likely, two 

 or more distinct amoebulse become associated to form a plasmodium, then 

 the two nuclei of the gametocytes in Disporea, of the " pansporoblast " of 

 Polysporea, may well be of distinct parentage, and in that case the sexual 

 process is not autogamous. 



Comparing the different modes of spore-formation, it is seen that 

 in all cases alike the spore arises from a sporoblast which divides 

 into several cells : two to form the sporocyst, which consists of two 

 distinct valves meeting in a suture, and thus defining a sutural 

 plane in the spore ; two (or four in Chloromyxidce) to form the 

 polar capsules ; and a fifth to furnish the binucleate sporozoite. 

 The spores of Myxosporidia have, as has been seen, a complex 

 structure, and are highly characteristic bodies the original psoro- 

 sperms of Johannes Miiller. In minor details of form and structure 

 they vary enormously in different species. The greatest diameter 

 of the spore may lie in the sutural plane, as in Polysporea generally, 

 or in a plane at right angles to it, as in Disporea (Fig. 169). The 

 sporocyst may be prolonged into tails and processes of various 

 kinds ; the polar capsules may be close together at one pole of the 

 spore, or at opposite poles. In all cases, so far as is known, the 

 spores germinate in the intestine of the new host, which becomes 

 infected casually by taking in the spores with its food. Other 

 methods of infection have been imagined, but have never been 

 demonstrated experimentally. 



The most complete account of the germination of the spore and of the early 

 development of the parasite in its new host is that given by Auerbach (758) 

 for Myxidium bergense, parasite of the gall-bladder of Oadus virens. The 

 spores from the gall-bladder pass through the rectum to the exterior. To 

 develop further, they must be taken up by the new host, in the stomach of 

 which, however, the spores undergo very little change ; the sporozoite rounds 

 itself off, and in some cases its nuclei copulate, in others they remain apart. 

 From the stomach the spores pass into the duodenum, and as soon as they 

 are acted upon by the bile the polar filaments are extruded, the valves of the 

 sporocyst split apart, and the amoeboid sporozoite creeps out. When the 

 amoebula becomes free, its two nuclei fuse into one if they have not done so 

 already. 



The free amoebula wanders actively up the bile-duct, and penetrates into a 



cell of the lining epithelium. Within the cell the nucleus of the parasite 



undergoes a change, becoming looser in texture. The amoebula leaves the 



cell and becomes free in the bile again, where it multiplies by fission, producing 



in this way very numerous amoebulae, which may occur singly or in clumps. 



