SPOROZOON PARASITES OF FISHES. 213 



Fig. 12. A section cut diagonally through a muscle fiber. This fiber is adjacent to the dermis. 

 On the inner side the sarcoplasm is hypertrophicd, on the outer side it retains the fibrillation. The 

 oval bodies arc interpreted as trophoplasms of the M. musculi. The large one has several spherical 

 bodies which take a deep ha?matein stain, presumably nuclei. (X800.) 



Fig. i,s. a muscle fiber in which there are the first evidences of disintegration. It contains two 

 or more large trophoplasts or schizonts. The appearance of the cy-toplasm is like that of other 

 stages, pale and unstained, there being no sign of the nucleus. There is evidence of a complex system 

 of pseudopodial extensions of the cytoplasm which is characteristic of the Myxosporidia. Large indi- 

 vidual 84.7/; by 192.5/!. (X400.) 



Fig. 14. Multiplicative spores of A/. musctiU, presumably derived from a large trophoplasm such 

 as figure 13. There is no cyst wall. In adjacent sections are fragments of the schizont nuclei mingled 

 with the spores. The spores stain feebly with eosin and orange G. The nuclei are not stained deeply. 

 19. 3/i in diameter. (X860.) 



Fig. 15. A mj-xoplasm of M. musculi in muscle from a smear preparation fixed with absolute alcohol 

 and ether and stained with methylene blue. One side overlies a nucleus of the muscle fiber. The 

 pale bands of the muscle fiber may be seen. The muscle stained deeply and the parasite pale. The 

 protoplasm is finely granular and there is only a suggestion of a cytoplasmic network. The nucleus is 

 vaguely stained. 13.4/1 by 18. 6/l(. (X2000.) 



Fig. 16. Formation of sporoblasts of M. musculi. This cyst is one of a mass numbering several 



hundred which occupy a position where a muscle fiber has been completely destroyed. The 10 spores 



stain very feebly. They lie in slight cavities of the protoplasm. Diameter of cyst 12/i; length of 



spore 4/(. (X2000.) 



Plate XXI. 



Fig. 17. A possible microgaraete of M. musculi from amongst the numerous myxoplasms of muscle 

 fibers adjacent to that shown in figure 18. The motile shape of several such structures, the small 

 amount of cytoplasm, and close approximation to some of the large mjTcoplasms are noteworthy. (See 

 right-hand upper region of fig. 18.) 6.5/1 by 2. 2/1. (X2000.) 



Fig. iS. A section of a muscle fiber of Fundulus heteroclitus cut crosswise at a slight angle. The 

 scales in the region of this infection had dropped off, and the area was almost white, being slightly 

 discolored by blood. The tissue was fixed in corrosive sublimate and acetic acid and stained first in 

 Mayer's hsematein, then in methylene blue, later in eosin and orange G. One of the structures in the 

 sarcoplasm, that to the left in the middle, is the nucleus of a muscle fiber. The others are stages in 

 the propagative cycle of M. musculi, primary and secondary' sporoblasts. The large one in the middle, 

 at the top, is 12.6/t in length and 5.9/1 in width. (X860.) 



Fig. 19. Three young sporoblasts of M. musctdi from the smaller type of cysts represented in 

 figure 16, plate xx. Note the increase in the size of the nuclei. They are typically free from cyto- 

 plasmic stain. (See C./wmiM/i, fig. 31.) Lower individual 4,11 by 2. 5U. (X2000.) 



Fig. 20. A fresh sporoblast of M. musculi containing a spore which is almost mature. From a deep 

 cavity in the flesh back of the head. Interesting in connection with figure 26. (Free-hand drawing, 

 not to scale.) 



Fig. 21. Sporocyte of M. musculi expelled from pansporoblast. It forms the first stage in the 

 series represented by figiu-es 23, 24, and 25. The nucleus is small and faintly stained, as is the rest of 

 the cytoplasm. It has no external envelope. Diameter 11. 9/1. (X2000.) 



Fig. 22. A pansporoblast of M. mujculi (sporocyst) with two daughter cells, the nuclei of which 

 are undergoing autogamous conjugation. (X2000.) 



Fig. 23. A pansporoblast of M. musculi after the autogamous conjugation and subsequent division 

 of the nuclei. 



Fig. 24. A sporocyst of M. musculi which has been set free from the pansporoblast. Apparently 

 the sporoplasm remains attached to one myxospore (fig. 20), and the other is almost devoid of external 

 protoplasm. The two wall cells are clearly visible, but without nuclei. The capsule nuclei are prob- 

 ablyformed but do not stain. Oneof the 12 nuclei happens to be in a suitable condition to take the stain, 

 ii.g/iby 13.4/1. (X2000.) 



Fig. 25. A myxospore of .1/. musculi with a remnant of protoplasm. Two polar capsules are 

 beginning to form. (X2000.) 



