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AN ELEMENTARY TEXT-BOOK OF BIOLOGY. 



of the body (Fig. 10), not far from its margin, and is connected 

 with its fellow in the head and also by a transverse commissure 

 running across each proglottis near its posterior side. In the 

 young tapeworm, before any proglottides have been detached, the 

 two excretory trunks converge posteriorly and pass to a vesicle 

 which opens to the exterior by a terminal pore. Numerous 

 delicate excretory tubules appear to be present in the parenchyma, 

 and these communicate on the one hand with the main trunks, 

 while on the other they terminate in flame-cells, which probably 



ul. 



Fig. 10. TAPEWORM (after Sommer). Enlarged. Proglottis of T<rnia 

 mediocanel/ata, with developed sexual organs. t, Spermaries (testes) ; 

 v.d, spermiduct (vas deferens) ; p, penis, contained in cirrus sac ; 

 ov, ovary ; y.rj, yolk gland ; sh.g, shell gland ; lit, uterus ; sp, spermo- 

 theca ; v, vagina ; g. a, genital atrium ; ex, main excretory tube, with 

 valves, v; n, lateral nerve-cord. 



communicate with minute spaces in the tissues. These spaces 

 collectively constitute a body-cavity. The main excretory trunks 

 possess valves by which the fluid they contain is prevented from 

 flowing along them towards the front end. Xanthin (C 5 H 4 N 4 O ) 

 and guanin (C 5 H 5 N 5 0) are said to occur in this fluid. 



The complicated hermaphrodite reproductive system (Fig. 10) 

 of the tapeworm bears a general resemblance to that of the Liver- 

 fluke. (1) The male organs consist of an immense number of 



