35 6 HENRY LESLIE OSBORN. 



the fish which he examined, being 1.3-3 mm. long as compared 

 with 3.5-4 mm. in length according to Looss. 



The cysts occupy a space in the endomysium among the fibers 

 of the muscle of the host. As we do not possess many detailed 

 accounts of the structure of trematode cysts or their relation to 

 the host tissues, an account of the facts found in this case may 

 be of some interest. The following methods were employed. 

 The cyst was carefully separated by teasing away the surrounding 

 muscle fibers of a piece which had been fixed and hardened in 

 suitable reagents. The cyst was then cut open and the enclosed 

 worm removed, after which pieces of the w r all were submitted 

 to the action of various staining reagents and mounted for 

 microscopical study. In other cases the muscle and enclosed 

 cyst was sectioned serially. In such a series we have transverse 

 sections of the wall and the surrounding muscle tissue, and at 

 the ends of the series there are tangential sections which can be 

 compared with the flat preparation just mentioned. Figs. 3 

 and 4 are low- and highpower views of such sections, and they 

 show the structural factors involved. The muscle fibers are 

 bent around the cyst as seen on the sides of the section; those 

 in the center which seem to end abruptly at the surface of the 

 cyst do not in reality do so, but are cut off as they run out of the 

 plane of the section. The worm wholly fills the cavity of the 

 cyst, the very small space which is seen in the figure being easily 

 accounted for by the shrinkage of the worm. The structure 

 of the cyst is seen in Fig. 4 to be merely a membrane produced 

 by the condensation of fibrous tissue. There are the usual wavy 

 fibers, thinning out as they reach the endomysium, and contin- 

 uous with the fibers which fill in the spaces between the muscle 

 fibers, and between the fibers the customary flattened connective 

 tissue nuclei. The flat preparations and tangential sections 

 show very clearly that the cyst is supplied with a capillary 

 network derived from the vascular supply of the muscle, and 

 these capillaries and their contained blood corpuscles can be 

 recognized in the section of the wall as shown in Fig. 4. Looss 

 states ('85) that his observations led him to conclude that the 

 cyst is produced by the host and then lined by a second envelope 

 produced by the worm itself. "Darunter befinded sich eine 

 zweite Hulle, die, anscheinend ein erhartetes Secret, von dem 



