203 



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. Near this 

 point is situated a pair of large, 

 long, slightly twisted segmental 

 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 Echhirus con- 

 sists of two main vessels, i. e., 

 a dorsal and a ventral vessel ; 

 the former extending along the 

 alimentary canal, and sending 

 a branch to the proboscis, where 

 it divides into two branches, 

 each uniting with the ventral 

 vessel. The blood is pale yel- 

 lowish, with corpuscles. The 

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



Fig. 140 —Anatomy of Phascolosoma 

 Goutdii^ cut optiu, with the flapg pinned 

 down, oe, oesophagus ; ar, two short 

 muscles ; pr, two long ri^tractor mus- 

 cles; w, next to a dark line the right 

 side of the long oesopliagus indicatmg 

 the w&ter-vascnlar tube ; w, nervous 

 cord ; 5, segmental organs ; the long^ 

 twi-ted intestine returns, ending at a 

 Natural size. — Drawn by J. S. Kings- 

 ley. 



