150 PKACTICAL PARASITOLOGY 



rounded at the lateral edges. It is enclosed in a homogeneous cuticle of 

 moderate thickness, within which, with the aid of a strong glass, is seen 

 a second, thinner, homogeneous layer the basement membrane. This 

 is intimately associated with a thin muscular structure, composed 

 of transverse and longitudinal fibres, the ends of the longitudinal 

 fibres appearing in the transverse section as small bright discs. 

 Within this structure is the so-called subcuticular layer, composed 

 of spindle-shaped cells arranged radially, which, in the section, have 

 been split along the axis-line. These cells resemble epithelial cells 

 in their arrangement, but they do not constitute a true epithelium. 

 If very thin sections from an uncontracted proglottide are closely 

 examined, it will be seen that the cells are separated from one another 

 by parenchyma, and that they do not all lie at the same level. The 

 parenchyma itself is very difficult of examination, and its structure 

 is differently described by different authors. It fills the entire space 

 enclosed by the subcuticular layer, and in it are embedded the 

 calcareous bodies, the various organs, and the longitudinal muscles. 

 The longitudinal muscles are situated in the peripheral zone, and 

 their development varies in different species. Their inner surface 

 is everywhere bounded by transverse muscles, which enclose the 

 central field. The part of the section within the transverse muscles 

 is called the ''middle-layer," while that outside it is called the 

 "cortical layer." By treating the specimen with some acid solution, 

 the carbonate of lime which the calcareous bodies contain will be 

 released, and they will become clear. 



In addition to the muscles already described, single fibres running 

 in a dorso-ventral direction, with brush-like ends which reach the 

 basement-membrane, will be seen. These are the parenchyma 

 muscles. 



With the exception of the peripheral portions of the cirrhus, 

 cirrhus-pouch, and vagina, all the sexual organs of Taeniidae are 

 included in the middle layer. In Dibothriocephalus, the follicles of 

 the yolk-gland which are of considerable size and are equally dis- 

 tributed upon both sides lie outside the longitudinal muscles and are 

 also included in the cortical layer, which is, moreover, penetrated by 

 the uterine orifice. 



Sections of Tsenise will show the lumens of the excretory canals 

 (fig. 71). Two are placed at each lateral extremity of the middle 

 layer, the external tubes being larger than the internal ones. In the 

 neck and in young proglottides, these tubes are of equal diameter ; the 

 two inner ones, however, begin to decline with increasing growth and, 

 in the ripe segments, they have usually completely disappeared. 

 Externally to the larger tubes, on both sides of the middle layer, lie 

 the cut surfaces of the nerve-cords, accompanied, in each case, by two 



