222 



ZOOLOGY. 



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. iNear this 

 point is situated a pair of large, 

 long, slightly twisted segmental 

 organs(s)the free ends of which 

 flare slightly. The nervous 

 system («) 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 (■?»), 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. c, 

 a dorsal and a ventral vessel ; 

 „. , .. . , p „. , the former extending along the 



Pig. 14fi.— Anatomy of Phascolosoma o ^ 



cottWie, cut open wiih the flaps pinned alimentary Canal, and sending 



down. (¥, oesopha£;i]8 ; ar, two short ^ ' , ° 



muscles ; pi\ two long retractor raus- a branch to the proboscis, where 



clea ; v, next to a dark line the right . -,''-, . in 



side of the long cesopliagus indicating it dlVldeS mto twO branches, 

 the water-vascniar tube; n, nervous , . . ',i ti j, i 



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

 twisted intestine returns, ending at a i mi i i -i - i ^1 



Natural size. -Drawn hy J. S. King.s- VCSSel. ihe blood IS pale yel- 



'''■''■ lowish, with corpuscles. The 



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



