4 U. S. BUREAU OF FISHERIES. 



The coiled filament is indistinct but can usually be made out by 

 careful focusing. The nucleus of the capsulogenous cell can often be 

 distinguished attached to one side of the capsule. The sporoplnsm 

 is finely granular and fills practically all of the spore not occupied 

 by the capsule. Two nuclei are present, and the sporoplasm is often 

 more or less distinct!}- divided into two parts of approximately the 

 game size, each containing a nucleus. There is no evidence of the 

 presence of an*iodophile vacuole. The diameter of the spore is about 

 GjjL, that of the capsule 3ix. 



The spore was seen and figured by Thompson (1916). Plis Figure 

 8 is evidently that of a mature spore, the large eosinophile body being 

 the capsule. Thompson also found a spore shaped like a '' four- 

 pointed star with four polar capsules," which he thought might have 

 some relation to the " Avormy " condition of the flesh. These spores 

 are not uncommon in both " wormy " and "' mushy ■' halibut and 

 belong to an undescribed species of Chloromyxum, which evidently 

 occurs in the connective tissue in the form of " diffuse infiltration " 

 and has nothing to do with the " wormy " condition. 



The systematic relationship of this species is somewhat uncertain. 

 The vegetative stages and method of sporulation are very similar 

 to many of the Myxobolidse, but the structure of the spore is quite 

 different. Under the circumstances it seems best to assign this 

 species to the Sphaerosporidse, at least provisionally. In the writer's 

 opinion, the present classification of the Myxosporidia is unsatis- 

 factory in several respects, and it is hoped that the attention which 

 rhe group is receiving will enable a more logical rearrangement of 

 the genera to be made in the near future. 



Considering the abundance of the parasites, it is remarkable that 

 the muscle fibers show so little signs of injury. Only the infected 

 fibers appear to be affected in any way, and even in these the fibrils 

 do not seem to be seriously injured until the inclosed trophozoites 

 have reached a comparatively late stage of development. In late 

 stages there is a noticeable tendency for the fibrils to swell up and 

 undergo a hyaline degeneration (fig. 5), but no fibers have been ob- 

 served in which the fibrils were entirely destroyed. According to 

 Thelohan (1895) and Keysselitz (1908), a somewhat similar hyaline 

 degeneration is produced by My.i'oholus pfeifferl in the muscles of 

 the barbel. 



Since the spores are formed only within the muscle fibers and 

 apparently remain there indefinitely, it is obvious that they can 

 only be released by the death or injury of the host. From our 

 knowledge of the life cycle of other Myxosporidia Ave may assume 

 that the spores are taken into the digestiA^e tract of the halibut 

 Avith the food and germinate in the intestine. The minute amoeboid 

 sporoplasm then makes its way into the blood vessels and is carried 

 to the muscles, where it leaves the capillaries and enters the muscle 

 fibers. The large number of infected fibers indicates that, in all 

 probability, there is a multiplicatiA'e stage before the young 

 trophozoites enter the fibers. After entering the fibers the troph- 

 ozoites evidently divide several times, for in no other Avay can we 

 explain the presence of several trophozoites in each fiber. 



It is interesting to note that although a number of Myxosporidia 

 are knoAvn to occur in the muscles of various species of fish the great 



