23] PROTEOCEPHALIDAE — LA RUE 23 



stou (1909, 1911, 1912a). Outside of this genus the only other species 

 to have cuticular hooklets or spines is Proteocephalus osculatus, in which 

 they are reported to have been found on the apical fifth sucker. 



The parenchyma resembles that of other cestodes but is more loose 

 than in the Cyclophyllidean cestodes which the author has examined. 

 In the parenchyma the cell outlines are indistinguishable but there are 

 numerous structures present which look somewhat like minute fibrillae. 

 Large fat spaces are usually visible in the prepared sections and some- 

 times in toto preparations. In 0. filar oides studied by the author (1909) 

 the fat spaces are spheroidal or ovoidal in form and have a dimension of 

 0.03 to 0.045 mm. Similar spaces have been observed in other species of 

 the family. They are smaller in the fish cestodes studied and larger in 

 the snake and amphibian cestodes. The fat of fresh cestodes or of those 

 recently killed in formol is readily stained by osmic acid solutions or by 

 an alcoholic solution of Sudan III. Other specific fat stains have not 

 been tried. The character of the parenchyma affects the staining prop- 

 erties of the cestodes. Those cestodes having a loose parenchyma make 

 much better toto preparations than do those which have the dense 

 parenchyma. 



In general the parenchyma of the group of snake Proteocephalids 

 is a more open, looser network than that of the fish Proteocephalids. 

 There is more of the fibrillar structure present in the parenchyma of the 

 latter than of the former. Whether this character is correlated with 

 differences in environmental stimuli is not known. Perhaps the appear- 

 ances of the parenchyma of cestodes can be explained as are the appear- 

 ances of the connective tissues of higher animals. If this be true then 

 it is evident that the closer woven texture of the parenchyma in fish 

 cestodes is indicative of more frequent stresses and strains placed upon 

 the cestode by the activity of the host or by the movement of ingested 

 materials through the alimentary tract. 



The sub-cuticular muscles resemble those of other cestodes. The 

 circular and longitudinal fibers are not strong. Within the layer of sub- 

 cuticular cells of the strobila there is a layer of longitudinal muscle 

 fibers which separates the cortical from the medullary parenchyma in 

 which lie almost the entire generative organs. This layer of fibers forms 

 what is known as the inner muscle sheath. The sheath is well developed 

 in some species, particuarly in the larger species of fish Proteocephalids, 

 while in the weaker species and in Ophiotaenia especially it is poorly 

 developed. In these cases the muscles are few in number and separated 

 from each other by intervals. The muscles of the inner sheath pass 

 through the intersegmental septa. Other muscle fibers which pass 

 through the tissues of the proglottid from dorsal to ventral and from 



