114 Papers from the Marine Biological Laboratory at Tortugas. 



The ground color of the aboral surface of Pentaceros reticulatus 

 varies from light yellow to a very deep reddish-brown. The reticulation, 

 on the nodes of which the spines are situated, is brought into sharp 

 contrast with this ground by its usually lighter color. In all of the 

 specimens examined the aboral surface (fig. 6) was light in color with 

 strong, glistening spines bordering the ambulacral grooves. 



The body integument is extremely hard and tough. Removal of any 

 part of the wall is best accomplished by the use of a heavy, sharp scalpel. 



THE DIGESTIVE SYSTEM. 



The anus is large and distinct and may be seen without difficulty, 

 slightly to the left of a line which might be drawn through the mad- 

 reporic plate to the tip of the opposite arm. 



Upon removing the aboral wall one sees the short, cone-like rectum 

 (fig. 2, an.) which arises from the center of the broad, five-sided, pyram- 

 idal intestine. Into this large intestine open interradially the ducts of 

 the intestinal caeca (resp.), each of these ducts arising by the union of 

 the single ducts of the caeca of adjacent arms at the inner termination 

 of the interradial septa (i.p.). 



The intestinal caeca, two of which lie in each arm and whose ducts 

 reach the intestine as above described, are attached to the aboral body- 

 wall by strong muscular connections. The cajca consist of a single 

 main duct from which arise numerous bladder-like diverticula which are 

 capable of great distention. Upon opening some specimens the cagca 

 were found to be greatly distended. Upon stimulation they slowly 

 contracted, the entire organ shrinking to about one-third of its former 

 size. The contents were watery, although the inner wall of the caeca 

 was found to be slimy. 



Beneath the intestine, upon the surface of the stomach in each 

 radius, is what appears at first sight to be a second set of five caeca, 

 each made up of two parts. Further examination shows that these are 

 merely pouches formed by the folding of the upper wall of the pyloric 

 portion of the stomach. They involve the regions into which the ducts 

 of the pyloric cajca open and have a narrow slit-like connection with the 

 stomach. This connection may be greatly widened by straightening out 

 the folds. The pyloric caeca (pyl. caec.) are large and greatly branched. 

 In color they are brownish-green. 



The cardiac portion of the stomach (fig. 5, card, st.) is large and its 

 muscles, both those which are attached along the sides of the ambu- 

 lacral ridge (retr.) and those attached at the oral ends of the ridges, are 

 powerful. 



THE WATER VASCULAR SYSTEM. 



The madreporic plate (figs, i and 2, madr.) is inconspicuous but 

 may be recognized readily by its color which is lighter than the sur- 

 rounding ground color, From the plate the stone canal (mad. can.) 

 leads downward to the ring canal (r. c). From the ring canal are 

 given off the Polian vesicles, the Tiedemann bodies, the ampullae of the 

 first tube feet, and the radial canals. A large-stalked Polian vesicle 



