lander: anatomy of hemiurus crenatus. 5 



The longitudinal muscle fibres of Ogmogaster have been described 

 by Jiigerskiold ('91) as consisting of fibrillai, while he describes the 

 circular muscle fibres as showing a clear central area and a peripheral, 

 highly refractive portion, the same condition as that described above for 

 the longitudinal muscle fibres of Hemiurus crenatus. Walter ('93) 

 describes both the dorso-ventral muscle fibres and the muscle fibres of 

 the body wall as having a fibrillar structure. According to StaflTord's 

 ('96) account the dorso-ventral muscles of Aspidogaster have a fibrillar 

 structure, and also show in cross section a deeply staining peripheral 

 portion surrounding a less deeply staining core. 



There is a special development of muscle fibres in connection with the 

 preacetabular fossa. The structure consists of a mass of radially arranged 

 fibres between which is found a finely granular substance (Plate 3, Fior, 

 28). The greater portion of the structure lies anterior to the fossa. There 

 is no internal limiting membrane, as in the case of the suckers, and many 

 of the fibres pass out some distance into the parenchyma. 



Parenchyma. 



The parenchyma presents three principal modifications, a periph- 

 eral granular layer, a vesicular parenchyma, occupying most of the 

 space between the organs, and a cellular sheath found around the 

 intestinal coeca in the posterior portion of the body (Plate 2, Fig. 25). 

 The peripheral granular portion, or sub-cuticula, forms quite a distinct 

 layer next to the body muscles, and it fills in the spaces between 

 the muscle fibres. It appears to be rather irregularly but finely granular, 

 and is from one to three times as thick as the cuticula (Fig. 2b, pa'ench. 

 gran.). The layer as a whole shows no evidence of cellular structure, 

 but imbedded in it are numerous groups of nuclei, each group being 

 surrounded by a circumscribed mass of protoplasm (Plate 2, Fig. 25; 

 Plate 3, Figs. 29-31). In each of these clusters can be counted from one 

 to ten nuclei, the larger groups being the more common. In the majority 

 of cases each group appears to constitute a syncytium, but in many groups 

 the protoplasm is distinctly divided into cells (Fig. 31). Corresponding 

 to each group of nuclei there occurs a thickening of the peripheral granu- 

 lar layer, which protrudes into the vesicular parenchyma. Each nucleus 

 shows a large number of small deeply staining granules, which are 

 especially abundant in the periphery, and usually one much larger chro- 

 matic mass, the diameter of which may be one-fourth as great as that of 

 the nucleus. The protoplasm surrounding the nuclei is sharply marked 



