376 



ZOOLOGY 



SECT. 



the ambulacra! grooves and their offsets which extend throughout 

 the length of the arms and pinnules. In the axis of the support- 

 ing ossicles of the arm is an axial nerve (ax. co.\ which gives off 

 branches (Fig. 303, ax. ne.) running through the axes of the ossicles 

 of the pinnules. The axial nerves are connected internally, not 

 with the circum-oral nerve-ring, but with a central body situated 

 below the rosette, in the interior of the centro-dorsal ossicle. This, 

 the central capsule (Fig. 304, cent, caps.), forms the investment of 

 a body termed the five-chambered organ (chamb. org.\ divided into 

 five parts by radial septa, and continuous with the dorsal end of 

 the genital stolon. Processes from the five angles of the central 

 capsule combine to form a pentagonal ring from which pass out- 



len-l 



amb 



c7ux.mb.org 



cent, caps 



FIG. 304. Antedon, Diagrammatic view of a median vertical section through the disc, passing 

 through one radius and one inter-radius. aml>. ambulacral vessels ; ax. co. axial nerve cord 

 passing through the ossicles of the arm ; Br^ Br,* brachial ossicles ; CD. centro-dorsal 

 ossicle; cent. m/w. central capsule; clm;nl>. o/y/. chambered organ; cirr. cirri ;' ect. ne. 

 ambulacral (epidermal) nerve-ring and radial nerve ; (/en. st. genital stolon ; int. intestine '. 

 mo. mouth; /f,i R^ J{,3 radials ; ros. rosette; tent, tentacles; v:at. p. water-pores. (After 

 Mimes Marshall.) 



wards the axial nerves of the arms. The ambulacral nerves and 

 their central ring represent the epidermal nerves of the Starfish ; 

 the axial nerves are represented in the latter only by the com- 

 paratively feebly-developed coelomic system. 



A blood-vascular system is present, with a circum-oral rin| 

 vessel giving off radial vessels to the arms, and a plexus of vessel 

 surrounding the oesophagus, and enclosing the genital stolon. 



Numerous bodies termed the sacculi, the character of whicl 

 has given rise to much discussion, occur regularly arranged alon^ 

 the ambulacral grooves, and also in other parts. They are small 

 spherical bodies which become vividly coloured by means of 

 staining agents. They are sometimes supposed to be parasitic 



