SPOROZOON PARASITES OF FISHES. 203 



appear to be spherical in form (fig. 14, pi. xx) and vary somewhat in size. They have 

 a small faintly-staining nucleus and hyalin nonstaining cytoplasm. Isolated spores 

 and masses of spores recently discharged from the cysts also occur in the smear prepa- 

 rations associated with the intrafibrillar masses of material that appear to be equivalent 

 to schizonts. These spores also occur in small numbers in the diseased gill where 

 nivxospores and sporoblasts are to be found in very great numbers. 



The occurrence of a multiplicative process of reproduction amongst the Mj^xo- 

 sporidia in the manner here described is not uncommon. We have authentic cases 

 in gall parasites of the flounder, and they have been described in M. pjcifjcri (Keys- 

 selitz, 1908) and in Hcnncguya gigantca (Nemeczek, 191 1). While there is no question 

 but that there are multiplicative spores, our evidence that the spore here described 

 is such is, as with the trophoplasm, far from conclusive. Judging from the meager 

 e\'idence at our disposal, there is about equal reason for considering it a young sporo- 

 blast or a young trophoplast. It is more harmonious to regard these amoeboid spores 

 as the progenitors of both multiplicative and propagative trophoplasts and the oval 

 spores, which are described below (p. 204) as sporoblasts, more especially since they 

 apparently arise by free cell formation and in smaller numbers. 



The propagative and sporoblast stages have been encountered frequently in both 

 sections and smear preparations. One series of sections of diseased integument and 

 muscle (referred to on p. 198), which were cut approximately at right angles to the body 

 surface, contains numerous large cells (fig. 18, pi. xxi) with small well-stained (with 

 haematein) nuclei. Some of the muscle fibers are cut obliquely. They lie in the midst of 

 healthy tissue and under integument which is apparently healthy. These myxoplasms 

 are of oblong or spherical form with more or less even surface. The cytoplasm is 

 tolerably homogeneous and does not retain the stains. The karyoplasm is also unstained, 

 but the chromatin is somewhat conspicuous. These cells occur abundantly throughout 

 60 or more sections, in 6 to 8 adjacent fibers, also in other distant fibers. Upwards 

 of a hundred perfectly normal fibers around them have not a single foreign cell. Such 

 cells are always intracellular. The sarcoplasm is considerably modified. The fibrillar 

 structure is lost and the appearance is almost homogeneous. 



A cell similar in every respect to the myxoplasm just referred to, occurs abundantly 

 in smears of muscle tissues. It stains less readily than do leucocytes and has smaller 

 nuclei with less conspicuous chromatin. Myxospores and pansporoblasts have been 

 found in their midst, in fact are to be found on slides where this type of cell occurs and 

 not elsewhere. In this connection it is interesting, and perhaps additional evidence of 

 relationship, that the same sore from which the sections containing these myxoplasms 

 (fig. 18, pi. XX) were made also supplied a smear preparation containing numerous myxo- 

 spores and pansporoblasts represented in figure 26, plate xxi. The sporoblast resembles 

 the myxoplasm of smear preparations in shape, clear, nonstaining cytoplasm, size, and 

 feebly staining (with methylene blue) nucleus. It is for the above reasons that this 

 type is assumed to belong in the propagative cycle. 



There is a wide range of conditions to be seen in the nuclei of these myxoplasms, 

 as well as some variations in size. Some densely-staining, cigar-shaped bodies (fig. 17, 

 pi. XXI) almost devoid of protoplasm are embedded in the sarcoplasraa, and others are 

 closely appHed to the myxoplasms (fig. 18, pi. xxi, near right-hand upper corner). The 



