ENTOZOA. 



57 



pore, which is surrounded by the fibres of the suctorial organ. 

 The alimentary canal is continued from this pore for a very short 

 distance as a single tube, and then bifurcates ; the divisions {fig. 27. 

 c, c) diverge to enclose the bursa penis and the ventral sucker, again 

 approximate, and afterwards run parallel with each other, with a nar- 

 row interspace, along the middle of the body to the caudal extremity. 

 At their first bend, each tube gives off three or four branches from 

 its outer, but none from its inner side. The parallel tubes send off a 

 few short and simple branches from the inner side, and many larger 

 ramified branches from their outer sides, which terminate in blind 

 extremities near the margin of the body. 



These canals seem, at first sight, to be simply excavated in the 

 substance of the body ; but, attentively examined, they present a 

 delicate proper tissue. They are usually filled with a brownish 

 chyme, which appears to be mucus stained with cholesterine. 



A more minute system of ramified tubes, which by some have been 

 regarded as the nutrient vessels, commences by a small foramen at the 

 caudal extremity of the body. The trunk of this system runs forwards 

 with a serpentine course, along the interspace of the forked alimentary 

 canal, to the middle of the body, where it terminates in many finely 

 ramified branches. It seems to represent, therefore, an excretory 

 rather than a nutrient system. 



The vascular system of Diplostomum volvens, so beautifully illus- 

 trated by Nordmann, is surely the equivalent of the excretory system 

 of capillaries, described by Mehlis in the Distoma hepaticum ; and the 

 median trunk, which is compared by Nordmann to the dorsal aorta in 

 the Anellides, must be the principal excretory conduit : it passes 

 directly backwards to the terminal pore, distinctly recognised by 

 Nordmann in the Diplostomum as an excretory outlet ; and he does 

 not positively deny, what his figures indicate, its continuity with the 

 straight duct terminating at that pore. In the Dist. clavatum I have 

 shown that the excretory system is complicated by a large terminal 

 receptacle or bladder, of which the hinder pore is the outlet.* 



The male organs of the Distoma hepaticum consist of the se- 

 cerning seminal tubes, a vesicula seminalis, a penis, and its bursa : 

 the convoluted tubuli testis equal the smallest branches of the 

 alimentary canal in size ; they occupy a great extent of the middle 

 part of the body, are inextricably interwoven, are recognisable by 

 their opaque white colour, and terminate by two trunks in a common 

 canal, which ends at the base of the receptaculum penis. This 



* Zool. Trans. 1. p. 41. fig. 18. g. 



