528 ECHINODERMATA ECHINOIDEA chap. 



the amoebocytes floating in the general coelomic cavity. These 

 in part escape through the thin bases of the gills. In other 

 parts of the body they seem not to succeed in reaching the 

 exterior at all, but to degenerate and to form masses of pigment ; 

 the colour of the animal is largely due to these excrementitious 

 substances. 



The reproductive system, as in the two preceding orders, 

 consists of a vertical pillar, the " genital stolon," and a circular 

 " genital rachis " giving off interradial branches from which the 

 genital organs bud. The genital stolon is developed from the wall 

 of the general coelom near the upper end of the axial sinus ; it 

 attains a great development and ultimately completely surrounds 

 the axial sinus, which then appears like the cavity of a glandular 

 tube, the walls of which are constituted by the genital stolon. 

 The compound structure consisting of stolon and axial sinus was 

 actually described as a nephridium by the Sarasins 1 in the case 

 of Asthenosoma. Its true nature, however, is shown when the 

 upper end is examined ; it is then seen to open into the stone- 

 canal and to be in communication with the ampulla, into which 

 the pore-canals open. Lying alongside the upper end of the 

 axial sinus is the somewhat elongated " madreporic vesicle," or 

 right hydrocoele, which was described by Sarasin as the accessory 

 kidney (Nebenniere), since like the axial sinus it is partly 

 enveloped by the genital stolon. Leipoldt, 2 however, showed 

 clearly that it is a completely closed space. 



The genital rachis springs from the upper end of the stolon, 

 and as in Asteroids, it lies in the outer wall of a space called the 

 " aboral sinus " (Fig. 234, 20) intervening between it and the test. 

 In adult specimens it seems to degenerate. The genital organs 

 are situated at the ends of five interradial branches of the rachis 

 (Fig. 231, gon). Each is an immense tree-like structure consisting 

 of branching tubes, which are lined by the sexual cells. So 

 enormous do they become in the breeding season that they form 

 an article of food among fishermen. The term esculentus is 

 derived from this circumstance. Other species are regularly sold 

 for food as Frutta di Mare (Fruit of the Sea) at Naples, and 



1 E'rgebnisse naturwissenschaftlicher Forschungen auf Ceylon, 1887-1888, Bd. i. 

 Heft 3, pp. 105 et seq. 



2 "Das angebliche Excretionsorgan der Seeigel," Zeitschr. wiss. Zool. lv. 1893, 

 p. 585. 



