Introductio7i to Animal Morphology . 



173 



The water- vascular system con- Fig- 24. 



sists of two lateral, non-retractile, 

 ciliated vessels, opening behind 

 by a common pore, or separately 

 (Tristomum). There may be a 

 contractile, non-ciliated sac at the 

 junction of the two tubes (Fig. 

 24, y"), or they may be united in a 

 ring (D. rachieeum), or may form 

 a fine netted canal system (D. 

 dimorphum). The contents are 

 water, guanin, and calcareous con- 

 cretions. The circulatory system 

 is rarely definite. Tristomum 

 papillosum has a median tube, 

 giving off lateral branches. Small 

 (poison r) glands surround the an- 

 terior sucker, and open outside anterlor^^uck^rT/rportirior 



.1 i 1 o 1 1 , sucker ; c, intestine ; d, yelk 



the mouth. Some larvae and ecto- giand ; e, uterus ;/, porus ex- 



, . , . cretorius of (h) the water- 



paraSlteS ( AmphlStOma SUb-ClaVa- vascular system ; ^, oviduct ; 



z', ovary; /5r, cirrus in its pouch; 



tum and Dactylogyra) have black i, testis. 

 pigment flecks (eyes) in some cases, with rudimental, 

 crystal cones. The sexes are separate in Gynoecophorus, 

 Distoma filicolle, Wedlia bipartita ; others are herma- 

 phrodite. The female organs are, a germ-gland, two 

 yelk glands, an oviduct, uterus (a long coiled sac), 

 an azygos shell-gland, a vagina, and a receptaculum 

 seminis. In D. hepaticum, the common duct, before 

 it ends in the shell-gland, sends a duct backwards ta 

 the surface. The male organs are two rounded, tubu- 

 lar testes, a vas deferens, vesicula seminalis, and an 

 ejaculatory duct, ending in a penis (cirrus), which is 

 protrusible from its pouch. Sometimes a canal runs. 



