248 SOME MINUTE ANIMAL PARASITES 



submucosa. The spores of the Myxidium in the above 

 marine fishes at first are rounded and uninucleate. 

 They then become elongate and oval (Fig. 45, B). 

 The nucleus multiplies, and gradually two valvular 

 nuclei are produced, under whose influence the two 

 valves of the sporocyst appear, while simultaneously 

 two other nuclei control the formation of the two 

 polar capsules. These latter structures at first appear 

 as tiny oval or rounded refractile spots (Fig. 45, 

 A, y.s.). They increase in size and refractivity for 

 some time, and gradually become ovoid. The polar 

 filament forms and often protrudes slightly from the 

 capsule. The polar capsules are not exactly opposite 

 one another, and this slight asymmetry is marked by 

 the protrusion of the end of the filament, the ripe 

 spore presenting an appearance very like that of a 

 lemon. 



The method of infection has also been shown 

 experimentally by the same workers to be by the 

 contaminative method by the mouth. Bred fish 

 from, known clean stock have shown intense infection 

 in about three weeks after feeding on food con- 

 taminated with the spores of the Myxidium, taken 

 either from the gall-bladder or from the excrement 

 of an infected fish. The spores are passed through 

 the alimentary canal unchanged until they reach the 

 junction of the pyloric caeca and the intestine, and 

 there the powerful digestive ferments cause the open- 

 ing of the valves, and the contained amoeboid germs 

 escape to pass up the bile-duct into the gall-bladder, 

 where they grow for a time and then proceed to form 

 spores. 



