THE MYXOSPORIDIA 



755 



Myxosporidium 

 Cyst developed 



cysts on the gill-slits, urinary bladder and swim-bladder, in the spleen, liver, 

 etc. 



If a small cyst 2-6 mm. long be transferred to a slide and examined 

 under the microscope it will appear in the fresh unstained condition to consist 

 of an enveloping membrane and its contents. The 

 envelope is tough, thick, and amorphous, while the 

 contents consist of a more or less liquid material 

 (stained with hsematoidin in arterial cysts) contain- 

 ing various granules, as well as parasites in different 

 stages of development. 



Sections of the internal organs (liver, kidney, etc.) 

 should be fixed in osmic acid or perchloride of 

 mercury and stained with safranin or gentian- violet 

 and eosin (Wosielewski) : carbol-thionin is equally 

 useful. 



Morphology. The parasites are often rounded 

 and vary considerably in size (65-300/x) : their 

 protoplasm is finely granular. When examined in 



fish urine they exhibit very slow movements ; these in the wail of the mesenteric 

 are not apparent when the parasites are examined 

 in water. 



In the parasites as just described there appear at a given moment small 

 rounded structures containing one or two nuclei ; these constitute the primitive 

 spheres in which the spores are formed (Laveran). Each sphere gives rise to 

 two spores and some fatty granules which stain with osmic acid. The structure 

 of the spores is complicated and varies in the different species ; in size they 

 vary from 8 to 36/*. A spore consists of an enveloping membrane and its 



contents : the membrane of the en- 

 velope is formed of two transparent, 

 homogeneous valves applied one to 

 another like the two halves of a 

 walnut-shell. At one of the poles of 

 the spore there appear one to four 

 vesicles or polar capsules, which stain 

 with methylene blue, thionin or safra- 

 nin. These polar capsules each elon- 

 gate into a small canal and become 

 attached to the wall of the spore at 

 the pole, where a very fine opening 

 communicating with the exterior is 

 formed. 



Each polar capsule contains a 

 spirally- twisted filament which is very 

 difficult to see under natural con- 

 ditions, but if the preparation be 

 treated with a drop of glycerin or 

 potash solution the filaments suddenly 

 unroll themselves and project from 

 the spore; these filaments are occa- 

 sionally very well developed and may be eight to ten times the length of 

 the spore (fig. 357). Besides the polar capsules, the spore contains an 

 homogeneous protoplasm and a centrally-situated nucleus which can be 

 stained with safranin. 



The spore constitutes the means by which the parasite is conveyed from 



FIG. 357. Myxosporidium of the tench. Mal- 

 pighian corpuscle containing a Myxosporidium. 

 Various forms of spores contained in the corpuscle : 

 above, immature amoaboid spores ; to the right, 

 immature spores. (After Balbiani.) 



