224 



PLATYHELMINTHES. 



muscular pharynx with a more or less elongated oesophagus (Fig. 

 177), which is prolonged into a forked intestine, ending blindly 

 and often beset with coeca. The organs are embedded in a paren- 

 chyma of muscle and connective tissue. 



The excretory apparatus consists of two large lateral trunks, 

 and of a network of fine vessels permeating the tissues and ending 

 in small ciliated lobules (flame-cells). The two large trunks usually 

 open into a common contractile vesicle, which opens to the exterior 



at th$ hind end 



of the body. 

 The nervous 



system consists of 



a bilobed ganglion 



lying above the 



oesophagus. From 



it there pass out, 



in addition to 



some small nerves, 



two strong back- 



wardly directed 



ventral nerve- 

 trunks. These 



are connected by 



transverse anasto- 

 with each 

 and with 



two weaker lateral 



longitudinal cords, 

 which are themselves connected with two dorsal FlG - ire. -Nervous system 



.of Distomum isostomum 



trunks (Fig. 178). Eye -spots with refractive (after E. Gam-on). MS 

 bodies are sometimes present on the larvae 

 during their migration, and in many of the 

 ectoparasitic forms. 



Locomotion is effected by the dermo-muscular system, with the 

 co-operation of the organs of adhesion (suckers and hooks) which 

 present numerous modifications in number, form, and arrangement. 



The organs of adhesion, in size and development, are related to 

 the endoparasitic or ectoparasitic mode of life. In the endo- 

 parasitic Trematodes they are less developed, and usually consist 

 of the oral sucker and of a second larger sucker on the ventral 

 surface, either near the mouth as in Distomum, or at the opposite 



FIG. 177. Young Distomum (after la 

 Valette). Ex trunk of the excretory 

 system ; Ep excretory pore ; mouth other, 

 with sucker ; S ventral sucker ; P 

 pharynx ; D forked intestine. 



oral sucker; Bs ventral 

 sucker ; Sn lateral nerve ; 

 En dorsal nerve; Bn 

 ventral nerve. 



