202 BULLETIN OF THE BUREAU OF FISHERIES. 



Certain fish in which the diseased parts were conspicuously congested (ventral part of 

 the head, around the anus, and about the eyes) were almost invariably found to con- 

 tain a large number of myxospores. When we consider the unknown stages of the 

 Sporozoa which, according to the cyclic habit of these organisms, advance from stage 

 to stage in a given culture at nearly the same rate, there is reason to attribute to them 

 more destruction than our observations warrant. Our present lack of knowledge is no 

 doubt due in part to the inadequate stains that have been employed and in part to the 

 confusion of tissue cells with certain stages of the myxosporidian cycle. (See also p. 205.) 



STAGES OF MVXOBOLUS MUSCULI. 



Mention is made in the literature of but one other case of mxyosporidian disease 

 of the integument and flesh which is closely allied to that of the Fundulus, namely M. 

 lintoni of Cyprinodon varicgatiis (Linton, 1889-1891). With this one exception, similar 

 diseases in other American and European salt-water minnows, as far as we can learn, 

 have not been described. The M. lintoni of the Cyprinodon was at first supposed to be 

 identical to the M. musculi of Fundulus. But very recently a tumor of the variegated 

 minnow was encountered. (See p. 206.) Both the spore and the tumor are markedly 

 different from the common condition of Fiinduhis. 



The mj-xoplasm of M . musculi produces a great many pansporoblasts, each with a 

 single spore. There is a large vacuole in most of the spores which is the characteristic 

 iodinophilous vacuole of the genus Myxobolus, to which the parasite undoubtedly belongs. 



Of the life history we have the spore, pansporoblast, possibly the myxoplasm, 

 schizont, and multiplicative or autospore. In but 3 of the 18 fish which harbor Sporozoa 

 have we stages (figs. 20, 21, 26, 27, pi. xxi) that can be unmistakably connected with the 

 spore. By association in the same tissue or by the appearance and staining reaction 

 we have probably identified the m\Tcoplasms and autospores. 



According to Auerbach's (1910) description of M. bergense, the spore terminates 

 the life cycle in a given host and starts a new cycle in a new host. We can but assume 

 that the trophoplasm of M. musculi likewise arises in some way from a primary myxo- 

 spore. The trophoplasm (fig. 12, pi. xx) is difficult to stain, and therefore its sporozoon 

 properties are not always certain. (See also Chloromyxum properties, p. 205.) Spherical 

 or oval spaces in the diseased myoplasm and in the epidermal cells (possibly identical, 

 fig. 36, pi. XXI, and p. 197) are very abundant. These are probably multiplicative tropho- 

 plasms, unless we have confused them with fat or other nonstaining substances. Some- 

 times these bodies have nuclei (fig. 12) which, though usually faint, may stain deeply. 

 It is not impossible that some of these small trophoplasms may be those of the Chloro- 

 myxum. When large, the trophoplasms have a granular structure (fig. 13, pi. xx) and are 

 doubtless preparing to undergo schizogony. We have encountered but five or six 

 such schizonts. In one series of sections they are associated in diseased muscle fibers 

 with cysts containing many spores. (Fig. 14, pi. xx.) The amoeboid form of the mature 

 schizont is characteristic and distinguishes it from the smaller forms. The schizont 

 in figure 13 is 33/i wide by y^pi in length. Some of the cysts are about this size, but 

 figure 14, which is ig/i wide and 24/1 long, is a section through the small end of a cyst 

 of only moderate size. The cysts are found both within and between the muscle fibers. 

 They contain several hundred spores, the nucleus of which, like that of the trophoplasm, 

 has at times little afTmity for the stains we have employed. The spores sometimes 



