NO. 19.] ECHINODERMS OF CONNECTICUT. 25 



which form the skeleton of aboral and lateral surfaces of the 

 disk and arms are shown in Plate II. 



INTERNAL STRUCTURE 



If the body of a starfish be opened by removing with fine 

 scissors the body walls of the aboral surface of the disk and one or 

 more arms, as indicated in Plate V, the internal organs are easily 

 exposed. The most conspicuous viscera are the various portions 

 of the digestive system, and, in certain seasons of the year, the 

 reproductive organs. 



In the dissection shown on Plate V, the five cardiac pouches 

 of the stomach (c. c) lie beneath the five-lobed pylorus (p. c), 

 into which open the profusely branched digestive glands, pyloric, 

 or hepatic, caeca (h. c). The madreporic plate (m. p), rectal 

 caeca (r. c), ambulacral braces (a. o), retractor muscles of 

 stomach (r. m), vertebral ridge (v. r) and sexual glands (s. g) 

 are shown. In the lower left-hand ray the pyloric caeca are laid 

 aside and the sexual glands removed to show the ampullae of 

 the tube-feet on each side of the vertebral ridge. In the median 

 ray the hepatic caeca are removed completely to show the position 

 and extent of the sexual glands (s. g). 



Alimentary Canal. — The digestive system of the starfish is 

 modified to conform with the general shape of the body. The 

 small, centrally placed mouth leads by a short esophagus into 

 the spacious cardiac portion of the stomach. The latter is pro- 

 vided with five broad lobes, cardiac pouches, opposite the bases 

 of the five arms (Plate V). The walls are very thin, much 

 folded, and muscular, so that this portion of the stomach can 

 be completely everted from the mouth opening and wrapped 

 around such food as the animal secures. After the prey has been 



Explanation of Plate V. Anatomy of starfish, Asterias vulgaris. (Two- 

 thirds natural size.) 



Dissection from aboral surface to show internal anatomy; a. 0, am- 

 bulacral braces ; c. c, cardiac portion of stomach ; h. c, hepatic caeca ; m. A, 

 madreporic plate; p.c, pylorus; r.c, rectal caeca; r.m, retractor muscle; 

 j. g, sexual glands ; v. r, vertebral ridge. 



The lower right ray shows the viscera in their natural position. In 

 the lower left ray the sexual glands and retractor muscles have been 

 removed and the hepatic caeca separated to show the ambulacral ossicles 

 and ampullae of tube-feet. In the upper ray the hepatic caeca have been 

 removed. 



