168 SYNOPTIC COLLECTION. 



tinued from the stomach into each arm (No. 306). The 

 stomach is extended above into a short, indefinite intestine 

 which opens near the center of the aboral area. It does 

 not seem to be functionally useful and may be the remain- 

 ing vestige of the well defined anus of the Crinoids (Pack- 

 ard). Opening into the intestine is the liver which consists 

 of two long branches that extend into each arm (see No. 

 306). According to Griffith and Johnstone 1 the "saccu- 

 lar diverticula " of the starfish are not hepatic but pancre- 

 atic in function. On chemical analysis they find the secre- 

 tion is similar to that of the vertebrate pancreas. 



The reproductive organs ovaries or testes are on 

 either side of each arm (No. 308) and open by slits at 

 the base of the arms near their junction with the central 

 disc. 



No. 306 and also No. 307 are specimens injected with 

 blue colored fluid to show the water-vascular system, 

 which arises as an outgrowth from the digestive system 

 as is the case with the Ctenophora. It consists of the 

 madreporic body, a short canal called the stone canal 

 which extends to a circular ring around the mouth (cir- 

 cumoral ring) from which five radial vessels are given off, 

 one into each arm ; these in turn connect with the water 

 sacs or ampullae of the tube feet which are seen in No. 

 307 extending in rows to the tip of each arm. The true 

 vascular blood system is difficult to observe. The heart 

 or pulsating vessel runs parallel with the stone canal. 

 The body cavity is filled with a watery fluid containing 

 corpuscles evidently representing the blood of more spe- 

 cialized animals. There are also delicate, tubular organs, 

 described as dermal branchiae, extending from the dorsal 

 surface, which probably have a respiratory function; 

 sometimes these may be seen swollen with water. On 

 the dorsal side there are many minute pores through 

 which water may enter or leave the body cavity. 



1 Proc. Roy. Soc. Edinburgh, XV, 1888 ; quoted in Amer. Nat., 

 XXIII, 1889, p. 1101. 



