PARORCHIS ACANTHUS, A NEW TREMATODE. 349 



ing the sucker. In sections the sucker has thus the appear- 

 ance of being separated from the rest of the body by a cavity 

 (Plate 21, fig. 2). In front of the ventral sucker the four 

 trunks are no longer distinguishable, but are represented by 

 a number of smaller vessels, which still retain their dorsal or 

 lateral position. A few of these small vessels extend as far 

 forward as the head. 



The system which has just been described probably cor- 

 responds to the usual simple Y-shaped or V-shaped excretory 

 vesicle. The remainder of the excretory apparatus does not 

 differ from that commonly met with. On each side of the 

 body there is a long narrow unbranched collecting tubule, 

 having a ventral situation not far to the outer side of the 

 intestinal diverticula. They are circular in section, and are 

 lined with flagella throughout the greater part of their 

 course. Their walls are distinctly marked, and differ in this 

 respect from those of the excretory trunks, which have the 

 appearance of being mere sinuses in the connective tissue. 

 The fluid in the vesicle and trunks is limpid, and contains 

 comparatively few granules. In the living animal it can be 

 seen to be driven to and fro by the movements ol^ the body. 



I am not aware of any Distomid which possesses an ex- 

 cretory sj^stem exactly corresponding to this type. Cases in 

 which the limbs of the excretory vesicle are put into com- 

 munication with each other by means of anastomosing vessels 

 are not uncommon, but they are not of the same nature as 

 the present instance. A condition displaying more resem- 

 blance is found in Mesometra (Monostomum) orbicu- 

 laris (Rud.),^ in which there is on both dorsal and ventral 

 surfaces a system of anastomosing canals, mapping out little 

 polygonal masses of parenchyma. The form of the vesicle, 

 however, in this species differs entirely from that of 

 Parorchis. 



The musculature is not essentially different from that of 

 other forms already described. Beneath the cuticle there is 

 a single layer of circular muscles. This is continued round 

 ^ Cf. ' Bronu's Tliierreicli,' IV, Vermes I i, p. G50, pi. xxxi, fig. 3. 



