420 ZOOLOGY SECT. 



described in the account of the examples, into two portions, the 

 cardiac and the pyloric, the former giving off rive large rounded 

 radial diverticula the cardiac pouches or cardiac caeca, and the 

 latter five pairs of very long branched diverticula the pyloric 

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

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

 Anthenea, Figs. 313 and 315) the intestine has connected with it 

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

 in others (as in Asterias, Fig. 311) 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 coelomic or aboral. The epidermal system is 

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

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

 with 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 Echiuoidea, but well 

 developed in the Asteroidea, Ophiuroidea, and Holothuroidea. 

 Its general arrangement has already been described in the account 

 of the Starfish. The aboral system is best developed in the Crinoidea 

 and is absent altogether in the Holothuroidea. 



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. 381), 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 in general there are five pairs, 

 the ducts from which open usually on a special plate on the aboral 

 surface, but in one or two species on the oral surface. In Pentaceros 

 and some other genera the gonads are more numerous. In the 

 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 ten pairs of gonads or groups of gonads, a pair in the walls 

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

 Mit.s on the oral surface close to the mouth, lu the Holothuroideu 



