MYXOSPORIDIA IOQ 



three nuclei. The protoplasm subsequently gathers round each nucleus. 

 Of the three cells thus formed, which develop a shell on the exterior 

 surface, two pass into the polar body and one into the amoeboid germ, 

 the nucleus of which, sooner or later, again divides (fig. 52). 



In pansporoblasts with ten nuclei, four nuclei are left for each sporoblast 

 after the extrusion of two ; the protoplasm gathers round them in such a way 

 that it forms two mononuclear cells, the future polar bodies, and one binu- 

 cleated cell, the amoeboid germ. In those few cases in which twelve to fourteen 

 nuclei appear in the pansporoblasts four pole-capsules appear in each spore. 



FIG. 52. (a, b) Myxoproteus 

 ambiguus ; (a) sporoblast showing 

 position of the two polar capsules 

 and the sporozoit ; (b) pansporo- 

 blast with two older sporoblasts, 

 the rejected nuclei being between 

 them ; the nucleus in the sporo- 

 zoits already divided ; (c) mature 

 spore of Myxobolus cyprini (after 

 Doflein). 



The spores, no doubt, fulfil the mission of effecting transmission to 

 other hosts ; infection occurs by the ingestion of the parasites per os after 

 their escape by some means from their host. Thelohan (10) has demon- 

 strated that the shells of the spores soon open under the influence of 

 the intestinal juices, thus allowing the young myxosporidia to escape. 

 Their further history is unknown ; but it may be surmised that they either 

 travel direct to the organs usually affected (gall bladder, urinary bladder), 

 or are distributed in the body by means of the circulation. 



In a few species increase has been observed to take place by means of 

 division or budding, which leads to a more aggravated infection . of the 

 already affected host ; possibly this process (multiplicative propagation by 

 plasmotomy) is very much more frequent than we are aware of. 



FIG. 53. Spores of a myxosporidium from the gills 

 of Gobio ftuviatilis, the contents of which are escaping. 

 600/1. (after Biitschli). 



Whether there is copulation, and at which stage it takes place, is as 

 yet unknown. 



Myxosporidia are divided into two sections Disporea and Polysporea 

 according to whether they form only two or several spores during their 

 growth ; the former, up to the present, appear to consist of two genera 

 limited to fishes, which are easily distinguishable by the shape of the spores : 

 Leptotheca, Thel., with a rounded spore-shell, and Ceratomyxa, Thel., with a 

 very elongated spore-cell. The larger number of genera appertain to the 

 Polysporea, which are divided into three families : 



(1) Amoeboid-germ with a vacuole ( (a) With two pole-capsules Myxidiidce, 



the contents of which do notj 



stain with iodine. [(b) With four pole-capsules. Chloromyxidce. 



(2) Amceboid-germ with a vacuole stainable with iodine. Spores with two 



pole-capsules Myxobolidcs. 

 For further subdivisions the differences of the spores are principally utilised 



