400 



ZOOLOGY 



SECT. 



te.nl 



amb 



usal.p 



The nervous system consists of two perfectly distinct parts 

 superficial and axial or aboral. A superficial radial nerve-ring 

 (ect. ne) surrounds the mouth, and from it are given off a series of 

 nerves thickenings of the epidermis of the ambulacral grooves 

 and their offsets which extend throughout the length of the 

 arms and pinnules. In the axis of the supporting ossicles of the 

 arm is an axial nerve (ax. co), which gives off branches (Fig. 338, 

 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 cen- 

 tral OljIX'lll 



(Fig. 339, cent, 

 caps), forms 

 the i n v e s 1- 

 ment of a 

 body termed 

 the five-cham- 

 bered organ 

 (chamb. onj) 

 divided into 

 five parts by 

 radial septa, 

 and continu- 

 ous with the 

 aboral end of 



\\Q genital 



stolon. Pro- 

 cesses from 

 the five angles 



of the central capsule combine to form a pentagonal ring from 

 which pass outwards the axial nerves of the arms. This system 

 controls the movements of the arms. Aborally the central capsule 

 gives off nerves to the cirri. 



A system corresponding to the perihgemal system of the 

 Starfish is p esent, though reduced, and there is a highly-developed 

 and complicated lacunar or haemal system. 



Numerous bodies termed the sacculi, the character of which 

 has given rise to much discussion, occur regularly arranged along 

 the ambulacral grooves and also in other parts. These are small 

 spherical bodies which become vividly coloured when treated with 

 staining agents. They are essentially collections of amoeboid cells 

 which may represent reserve materials, stored up for the nutrition 

 of the animal, or may contain excretory matters. 



cha.7nlj.org 



f tit. caps 



FIG. 339. Antedon. Diagrammatic view of a median vertical section 

 through the disc, passing through one radius and -one inter-radius. 

 ami), ambulacral vessels ; ax. co. axial nerve-cord passing through 

 the ossicles of the arm ; -Br. 1 Br.- brachial ossicles ; CD centra dorsal 

 ossicle ; cent. caps, central capsule ; chamb. org. chambered organ : 

 cirr. cirri ; ect ne. ambulacral (epidermal) nerve-ring and radial 

 nerve ; gen. st. genital stolon ; int. intestine ; mo. mouth ; 7J. 1 /f. 2 

 R. 3 radials ; ros. rosette; tent, tentacles ; teat. p. water-pores. (After 

 Milnes Marshall.) 



