204 BULLETIN OF THE BUREAU OF FISHERIES. 



conditions suggest conjugation, but the stages are too few to indicate a succession of 

 events. One myxoplasm contains two oblong spores. Elsewhere, replacing a degen- 

 erated muscle fiber, are numerous small cysts {iiu in diameter) with eccentric nuclei, 

 which contain from four to ten or a dozen clearly defined oblong spores (fig. i6, pi. xx). 

 These spores are found abundantly in other fish. (Fig. 19, pi. xxi.) They appear to 

 arise by free cell formation. They are characterized by a transparency and a failure to 

 stain that recall both the trophic stages and the sporoblasts. The nucleus, however, 

 does stain faintly. It is quite large when the spores are set free. The latter measure 

 4/1 by 2.5/( and sometimes assume a spherical or amoeboid form. Between this condi- 

 tion and the mature sporoblast we lack recognizable connecting stages. They are 

 not far removed, however, from the latter, which are spherical cells with very large 

 nuclei. (Fig. 35, pi. xxi.) These occur in the gill above mentioned and have there been 

 definitely connected with the myxospore. The pansporoblast has been encountered, 

 along with spores and sporoblasts, in fresh smears of muscle. These are apparently 

 identically homologous to those described for M. pfeifferi in the gills of the barbel 

 (Keysselitz, 1908). If so, the sporogenesis there related would appropriately apply to 

 M. musculi. Many stages in the genesis of the spore are represented in one of our 

 smear preparations. These have propagative stages (Keysselitz, 1908) as follows: 

 First the sporoblast with large nucleus (fig. 35, pi. xxi) and two-parted pansporoblast 

 (sporocyst) (fig. 22, 23, pi. xxi), which, according to Keysselitz, arises after a process of 

 autogamous conjugation. The sporocyst apparently sets free the sporocytes before 

 sporogenesis has proceeded far (fig. 21, pi. xxi). Giemsa stain does not reveal all the 

 nuclei concerned in sporogenesis. Valve cells are formed (fig. 24, pi. xxi) before the 

 polar capsules appear as large spherical bodies (fig. 25, pi. x.xi). Later the myxospore 

 becomes elongated and tapered (fig. 20, 26, pi. xxi). Two preparations have multitudes 

 of immature spores. They are all free from the sporocyst protoplasm and have thick 

 valves. It is therefore rather perplexing to explain figures 20 and 26. Perhaps the 

 spore is about to be discharged in figure 20. Considerable variation in this respect 

 occurs amongst some of the gall Myxosporidia. 



There are myxospores in 12 of the 85 fish examined. In but 3 of these do they 

 occur in great numbers. With two exceptions (in diseased gills), the myxospores are 

 not assembled in a manner that would suggest their origin from cysts or masses of 

 pansporoblasts, as is common in other species of Myxosporidia. The two cases referred 

 to may not be interpreted as evidence of this condition, but rather that the pansporo- 

 blasts, where very numerous, have been packed close together. There are at least a 

 thousand well-stained spores in the preserv-ed tissues. Not one occurs in the 10 tissues 

 of which sections have been made. But those same tissues which contain spores have 

 supplied all the propagative myxoplasms. 



The myxospores are very small (fig. 28, 29, pi. xxi). They average 14.3// in length 

 and 6.7// in width. In one fixed individual the plane at right angles to that passing 

 through the polar capsules is presented. It measures 6.711 in thickness, from which 

 we conclude that they are approximately circular in section. But another fresh spore 

 was flattened in a plane perpendicular to that of the polar capsules and sutures to about 

 two-thirds its width (fig. 30, pi. xxi). The polar capsules of myxospores average 6. 5U in 

 length and 2u in thickness. When extruded the filament is three to four times the length 

 of the spore (fig. 29, pi. xxi). Coiled within the polar capsule, the filament makes from 



