,a,li 



PHYLUM ECHINODERMATA 395 



ial diverticula, the cardiac pouches or cardiac caeca, and the latter 

 giving off five pairs of very long branched diverticula, the pyloric 

 or hepatic ca3ca. The intestine is short and conical, and opens, in 

 all but a few, by an anal aperture. In some Asteroidea (as in 

 Anthenea, Figs. 283 and 284) the intestine has connected with it 

 a system of five elongated bifurcated inter- radial intestinal casca ; 

 in others (as in Asterias, Fig. 281) these are represented only by 

 two or three lobed diverticula. In one member of the class there 

 are also ten caeca connected with the oesophagus. 



In the nervous system of the Echinodermata three distinct 

 parts, the relative development of which differs in the different 

 classes, are to be recognised. These are the epidermal or super- 

 ficial, the deep, and the ccelomic. The epidermal system is wellf) 

 developed in all the classes : its principal parts are a circum-oral/ 

 nerve -ring and radial branches, but a plexus of nerve-fibres with7 

 occasional nerve-cells extends from it through the epidermis. In 

 the Ophiuroids the radial nerves and the ring nerve are similar 

 in their arrangement to what is to be observed in the Asteroids, 

 but are more deeply placed, being covered over by the investing 

 calcareous plates. The deep-lying nervous system is absent in the 

 Crinoidea, very feebly developed in the Echinoidea, but well 

 developed in the Asteroidea, Ophiuroidea, and Holothuroidea. 

 Its general arrangement has already been described in the account 

 of the Starfish. The coelomic system is best developed in the 

 Crinoidea and is absent altogether in the Holothurians. 



The sexes are distinct in all the Echinoderms, with one or two 

 exceptions ; but there is very rarely any trace of sexual dimorphism. 

 Asterina gibbosa, the Starfish the development of which has been 

 described (p. 358), is one of the exceptional hermaphrodite forms ; 

 the young animals of this species are male, producing sperms, but 

 at a later stage they become female and produce only ova. In the 

 family Synaptidae of the Apoda there are also numerous examples 

 of hermaphroditism, the animal at first producing ova, later only 

 sperms. In Amphiura squamata, an Ophiuroid, both ovaries and 

 testes are present at once. The gonads, ovaries or testes as the 

 case may be, are branching bodies inter-radial in position, and 

 usually in pairs. In the Asteroidea there are five pairs, the ducts 

 from which open usually on a special plate on the dorsal surface, 

 but in one or two species open on the ventral surface. In the S " 

 Echinoidea there are five ovaries or testes, the five ducts of 

 which open on the genital plates of the apical system. In the 

 Ophiuroidea there are five pairs of gemtai glands, a pair in the 

 wall of each of five genital bursce, which open on the exterior by 

 slits on the ventral surface close to the mouth. In the Holo- 

 thuroidea there is only a single branched gland, sometimes imper- 

 fectly divided into two, with a duct opening on the dorsal surface 

 not far from the mouth. In the Crinoidea the ovaries and testes 



