ORGANS OF DIGESTION. .1* 



solium (Fig. 116. C. a. a.) These lateral digestive and 

 contractile tubes communicate with each other by a trans- 

 verse branch (C. c. c. c.) at the lower end of each segment 

 where they are constricted and valvular, and they open 

 externally by one or more lateral orifices (116. C. h.) on 

 the sides of each division of the body. The dendritic 

 ramifications of the ovary (C. d.) occupy the central part 

 of each segment, and open externally beside the intestinal 

 pore (C. h.), by a small distinct genital orifice (C. i), from 

 which likewise extends a styliform tubular duct (C. k.) 

 considered as a male organ (C./.) Besides the delicate exterior 

 skin covering all these organs, there is an outer transverse 

 and an inner longitudinal layer of muscular fibres which 

 produce the varied movements of this aggregate animal, so 

 that each segment of the teenia, which worm often exceeds a 

 hundred feet in length, possesses all the requisite organs 

 for nutrition and generation, as an entire animal, and no 

 gastric enlargement is developed in the whole course of 

 this alimentary tube. The four cesophageal canals however, 

 of the tcenea dispar, descending from the four lateral 

 cephalic pores, unite together in the middle of the neck 

 to form one median canal, which enlarges in each division 

 of the animal, and passes thus sacculated and continuous, 

 through all the segments of the body. Besides the usual 

 lateral pores of the head a minute opening and canal are seen 

 in the apex of the prominent papilla in the middle of the 

 head of the botkryocephati, as in some of the tcenice. The 

 alimentary organs of the trematode worms are more ramified 

 and sanguiferous in their appearance than those of the ces- 

 toid entozoa; they commence by one or more orifices near the 

 anterior part of the trunk, and pass backwards ramifying and 

 anastomosing freely along the lateral parts of the body, des- 

 titute of an anal opening, as in the other parenchymatous 

 species. In the distoma hepaticum they form two parallel 

 trunks near the middle of the body, and ramify into minute 

 capillaries on the lateral parts, as they proceed tapering back- 

 wards to the posterior extremity of the animal. In the penta- 

 stoma they unite to form a single straight median canal in the 

 back part of the body ; so that we still observe the tendency 

 to form a simple longitudinal median canal in all these forms 

 of parenchymatous entozoa, as in the higher orders of this 



PART III. Z 



