Introduction to Animal Morphology. 



The water-vascular system con- Fi s- 2 4- 



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, f], or they may be united in a 

 ring (D. rachiaeum), 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- 



ior sucker, and open outside JS^S^^^A 



., 101 j sucker; c, intestine; <f, yelk 



the mouth. Some larvae and ecto- P i.m.i : *, utenu :/. pom 



>rius of (h) the u 



parasites (AmphlStOmaSUb-clava- rascular system; .c, ovidn.t ; 



. i irrus in its pouch ; 



turn and Dactylogyra) have black /. 



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



crystal cones. The sexes are separate in Gyncecophonis, 



toma filicolle, \\Vdlia bipartita ; others are herma- 

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

 unK, an oviduct, uterus (a long coiled sac), 

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



Luis. In 1). hepaticum, the common duct, be! 



ids in the shell-gland, sends a duct backwards to 

 tlv- surface, I he male organs are two rounded, tubu- 

 lar testes, a v.i 'niiialis, and an 



ulatory duct, ending in a penis (cirrus , which is 



;rusil>]<- from its pouch. Sometimes a canal runs 



