82 LECTURE V. 



parallel with each other, with a narrow 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 sub^ 

 stance 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 or terminates by a small 

 foramen at the caudal extremity of the body. The trunk of this 

 system runs forwards with a slightly serpentine course, along the 

 interspace of the forked alimentary canal, to the anterior part of the 

 body, where it bifurcates, and terminates in many finely ramified 

 branches : similar branches come off in pairs from, or terminate in, 

 the main canal. These vessels seem to be an excretory rather than a 

 nutrient system. They are beautifully figured by the ingenious ana- 

 tomist Blanchard, who has succeeded in injecting them independently 

 of the digestive canals.* 



The vascular system of Diplostoma volvens, so beautifully illus- 

 trated by Nordmann f, is the equivalent of the system of capillaries, 

 described by Mehlis in the Distoma hepaticum ; and the median 

 trunk {fig- 38, Z»), 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 {ib. h), distinctly 

 recognised by Nordmann in the Diplostoma as an excretory outlet : 

 and he does not positively deny, what his figures indicate, its con- 

 tinuity with the straight duct terminating at that pore. In the Disf. 

 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 secern- 

 ing seminal tubes, a vesicula seminalis, a penis, and its bursa : the 

 convoluted tubuli testis equal the smallest branches of the alimentarj'' 

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

 body, are inextricably interwoven, are recognisable by their opake 



* LXIX. pi. 36. and LXX. (1820), p. 305. taf. It. The idea of the natnrc and 

 function of these vessels, given in my former edition, p. 57, has been adopted by the 

 experienced Sicbold, XXIV. p. 136. " So glaiibc ich gchort das Gefiissnctz 

 welches Bojaniis aus Distomum hepaticum bcschroibt jencm Kxcrctionsorgans an." 



f LXXI. p. 37. taf. iv. fig. 6. % LXXII. p. 41. fig. 18. g. 



