PHYLUM PLATYHELMTNTHES 



259 



unicellular glands derived from the epidermis are frequently 

 present beneath the integument. 



In the Cestodes, as in the rfl 



majority of the Trematodes, no 

 definite epidermis is present. 

 The external layer, sometimes 

 divided into two or more 

 strata, is of a homogeneous bm 

 non-cellular character, and is 

 usually termed cuticle. Beneath 

 this is a thin layer of paren- 

 chyma, the basal membrane. 

 Beneath this again is a layer 

 of fusiform cells, narrow pro- 

 longations of which pass to the 

 cuticle, into the inner part of 

 which they penetrate and 

 spread out into a thin layer. 

 These cells are by some authors 



d.vrn. 



rh.c 



FIG. 212. Section of the body-wall of a Triclad. 



regarded as the Cells that b. m. basement membrane; c. m. circular 

 , ,1 , 1 -I layer of Jmuscle-fibres ; d. v. m. dorse-ventral 



Secrete the CUtlCle ; but they la y er O f muscle-fibres ; e.l. m external longi- 



may be concerned in the 



tudinal layer of muscle-fibres ; ep. epidermis ; 

 i. 1. m. internal longitudinal layer of muscle- 



of nutrient matter, fibres ; p. parenchyma ; rh. rhabdites ; rh. c. 

 t , , rhabdite-forming cells. (After Jijima.) 



and some of them are un- 

 doubtedly of the nature of nerve-cells and have nerve-fibres 

 connected with them. 



The muscular layers of the body-wall vary somewhat in their 

 arrangement in the different groups of Platyhelminthes. Most 



commonly there aie 

 an external layer of 

 circularly arranged 

 and an internal layer 

 of longitudinally ar- 

 ranged fibres ; fre- 

 quently layers of 

 fibres running in a 

 diagonal direction 

 are present also. 



Characteristic of 

 the Flat-worms is a 

 peculiar form of con- 

 nective - tissue, the 

 parenchyma (Fig. 

 213) mention of 

 which has already 



FIG. 213. Parenchyma of Distomum. a, b. intercellular been made m the 

 spaces; bm. basement membrane ; c. nuclei ; d. nuclei ; / q oe T ,i T ,fi r , ric ~f +>. 

 ep. epidermis. (After Braun.) descriptions Ol tfce 



s 2 



d 



