22 CONNECTICUT GEOL. AND NAT. HIST. SURVEY. [BuU. 



efforts remove any small foreign body from the surface of the 

 disk or arm and thus serve to keep the body clean. They also 

 serve to protect the delicate skin from attacks of such small 

 enemies as might otherwise cause serious injuries. 



In the blood starfish (Henricia) pedicellarise are absent, the 

 body in this instance being protected by the multitude of closely 

 set spines (Plate I, figs. 1 — 3; Plate XI), which cover all 

 parts of the aboral surface. 



Mouth. — Turning now to the oral surface of the body, the 

 mouth may be seen to occupy the central portion of the disk. 

 Surrounding the mouth are five groups of movable spines (oral 

 spines, or mouth papillae), forming the five angles of the mouth 

 (Plate VIII). By means of muscular contractions the oral 

 spines may be brought together to close the mouth opening, or 

 may be opened widely to allow the extrusion of the stomach, as 

 indicated in the two photographs on Plate VIII. 



Tube-feet. — Extending outward from the mouth are five 

 deep grooves, the ambulacral grooves, one of which occupies 

 the oral surface of each arm (Plate IV). In these grooves are 

 situated the locomotor organs of the starfish, consisting of a 

 multitude of finger-like sucking tubes — the tube-feet — ar- 

 ranged in definite rows throughout the length of the arm. In 

 the species of Asterias (Plates IV and IX) there are four such 

 rows of tube-feet, while in Henricia (Plates I and XI) there are 

 but two. The rows are placed symmetrically on each side of 

 the axial line, as shown in Fig. 2. 



Each tube-foot consists of a muscular tube with a circular 

 disk at the free end (Fig. i). The tube leads between the os- 

 sicles forming the roof of the ambulacral groove, and connects 

 internally with a sac-like swelling — the ampulla, — and also, 

 by a narrow tube, with the radial canal of the water-vascular 

 system. The relations of these parts are shown in Fig. i. 



Plate IV- Oral surface of starfish, Asterias forbesi. (Natural size.) 



The ambulacral grooves are widely opened, disclosing the four rows 

 of crowded tube-feet, each with its terminal sucking disk. In the center 

 of the disk appears the delicate, baglike stomach, partially everted, as in 

 the beginning of the act of feeding. The photograph shows two rows 

 of slender adambulacral spines along the borders of the ambulacral grooves, 

 and the large blunt spines, surrounded by minute pedicellariae, nearer the 

 sides of the arms. 



