206 BULLETIN OF THE BUREAU OP FISHERIES. 



preparations that have been examined, we are inclined to consider the Myxobolus more 

 abundant and therefore the more common causal agent. 



The myxospore of C. funduli is about 7.5^ in diameter, with a polar axis somewhat 

 shorter (6^). At right angles to the polar axis, it is circular. There are four polar 

 capsules, which taper to the apex of the spore, curving so as to conform to the constric- 

 tion of the spore, which provides it with a blunt pointed apex (fig. 31 , 34, pi. xxi). There 

 are four conspicuous nuclei (black), one near the base of each polar capsule. The sporo- 

 plasm is stained a pale blue by the Giemsa. The polar capsules do not stain (fig. 31, 34, 

 pi. xxi) . There are occasional myxospores of considerable size to be seen inside the sporo- 

 blasts when the latter do not take up a particle of stain. Such clear hyalin amoeboid 

 pansporoblasts are numerous throughout the sarcoplasm. They vary in size from a 

 diameter of about 2fs to four or five times the diameter of the spore. 



PROTOZOA RELATED TO THOSE HERE DESCRIBED. 



Numerous Myxosporidia parasitic upon either integument, gill epithelium, con- 

 nective tissue, or muscle of fish have been described by other authors. About most of 

 them we have very meager information. M. lintoni (Linton, 1889; Gurley, 1893) of 

 Cyprinodon -variegatus (short minnow), as already stated (p. 202), more closely resembles 

 the parasites of Fundulus than any other species of which we know. The difference 

 at first seemed to be slight and to be easily accounted for by a difference in the age 

 of the spores. But when a case of the Cyprinodon tumor was finally obtained and 

 examined, the indentity of the parasites in the two hosts, as well as the nature of 

 the lesions, was found to be different. The "irregular fungoid elevations," described 

 and figured by I^inton and observed again by the writer, are of the nature of cysts con- 

 taining spores, located in the integument, whereas the elevated scales in Fundulus are 

 due to an infection of the epidermis by bacilli and a subdermal atrophy of the muscle. 

 No tumor or spore-filled cyst has ever been encountered. The Cyprinodon tumor which 

 we examined developed in a comparatively short time, probably less than a week, 

 though the period can not be accurately stated. It caused the death of the fish the day 

 following that on which it was first noticed. After the death of the host, the tumor was 

 8 mm. wide by 10 mm. long, and caused a conspicuous elevation from the back of the 

 fish anterior to the dorsal fin, about 2 to 2^ mm. thick. It was of a yellowish-pink color 

 when seen through the slightly pigmented integument. The scales were practically 

 undisturbed and the integument was completely intact, in this respect differing remark- 

 ably from the Fundulus sores. Beneath the tumor, the flesh contained intrafibrillar 

 myxoplasms and sporoblasts with occasional spores, while the tumor itself was almost 

 wholly a mass of myxospores, the latter numbering millions. We have already described 

 (p. 197) a totally different condition in the Fundulus, resulting from the M. musculi. 



There is such a difference in the appearance (Linton, 1889, fig. 3) of the spores that 

 they are readily distinguished. One can not be certain, however, that such differences 

 are not due to the comparison of different stages in the development of spores of the same 

 species. We have shown that the spores of M. musculi grow longer as they mature and 

 the spore wall becomes thinner (p. 205) . This fact would explain in part the discrepancy 

 in the dimensions of the spores from the Fundulus and Cyprinodon. But, since the 

 spore of M. lintoni measures 13.9/i in length, iifi in width, and S/t in thickness (at right 



