160 



ZOOLOO Y. 



insertion of the muscles it enlarges, but there is no true 

 stomach ; it is about twice the length of the body, and is bent 



and twisted on itself, ending 

 dorsally in a vent marked by an 

 external wart, on the anterior 

 third of the body. Near this 

 point is situated a pair of large, 

 long, slightly twisted segmcntal 

 organs(s)thefree ends of which 

 flare slightly. The nervous 

 system (n) forms an oesophageal 

 ring, and from it passes a well- 

 marked ventral single cord, 

 from which at short intervals 

 pass off small short lateral 

 nerves. The vascular system 

 is represented by a circular 

 vessel lying next to the ner- 

 vous oesophageal ring, sending 

 branches into, or at least in 

 communication with, the cavi- 

 ties of the tentacles, and from 

 the ring passing along and in- 

 timately connected with the di- 

 gestive tract, forming a ruffle- 

 like organ (v), ending at a point 

 nearly opposite the vent (a). 

 Prof. Greef finds that the vas- 

 cular system of Echiurus con- 

 sists of two main vessels, i. e., 

 a dorsal and a ventral vessel ; 

 the former extending along the 











Fig. 110. Anatomy of Phascolosoma 



Gouii/u, cut open, with the flaps pinned alimentary canal, and sending 



down, ce, oesophagus ; ai\ two short 



muscles ; pr, two long r.-tractor mus- a branch to the proboscis, where 



cles ; , next to a dark line the right .,.._. , 



side of the long oesophagus indicating it divides into two branches, 

 the water-vascular tube; n, nervous , ... .,, ,, 



cord; s, segmental organs; the long, each Uniting With the VClltral 

 twisted intestine returns, ending at a rm 11 i i 1 



Natural size.-Drawn by J. S.Kings- VCSSel. lllC blood IS pale yel- 



lowish, with corpuscles. The 

 blood-system of the Gephyrea, then, is homologous with 



