VIII ECHIN0DERMATA—8ACCULI OF CRINOIDS 489 



In this glandular layer the cells can no longer be recognised except by their 

 nuclei, no boundaries being distinguishable. The layer is closely packed with 

 secreted granules. Wandering cells and calcareous corpuscles are found in the con- 

 nective tissue wall. 



The animal, when irritated, vehemently ejects its Cuvierian organs through the 

 cloaca. (The susceptibility to irritation which leads to such ejection varies greatly 

 ill different forms.) In this process the tubes are not turned inside out, but are 

 thrown out complete, just as they are in the body cavity, probably through a rent 

 in the cloacal wall. When these tubes are thus thrown out, water is almost certainly 

 pressed out of the respiratory trees into their axial canals. The discharged Cuvierian 

 organs are remarkable (1) for their extreme viscidity; (2) for their extraordinary 

 extensibility. They can be drawn out to more than thirt}' times their ordinary 

 length. Their viscidity is no doubt produced by the secreted granules of the 

 glandular layer. In consequence of these peculiarities, the discharged Cuvierian 

 organs are weapons of defence ; they remain attached to the body of an enemy, and 

 impede its movements. They may also be weapons of attack, the prey being 

 caught and held fast till it dies, when its decomposing remains serve for food. 



The non-glandular Cuvierian organs are either tubular, like the glandular, or 

 branched. They are mostly beset with stalked vesicles. The smooth endothelium 

 of the body cavity which covers them shows no glandular development of any sort. 

 The part played by these non-glandular and consequently non-viscid organs is 

 entirely problematical. 



XVII. Excretion. 



Special excretory organs are altogether wanting throughout the 

 Echinodermata. It is probable that tluid excrement is osmotically 

 given off, together with the carbonic acid, at the respiratory surfaces 

 of the body. Fvirther, coloured and occasionally crystalline corpuscles, 

 which are met with in very different parts of the body, chiefly in 

 the connective tissue layers in most Echinoderms, have been regarded 

 as products of excretion. They appear to remain in the places of 

 their formation, this conclusion being arrived at from the fact that 

 they are present in far greater quantities in old than in young animals. 

 They are also found within the wandering cells, and it might be 

 worth investigation whether these wandering cells, which force their 

 way into the body- and the intestinal-epithelium, do not play some 

 part in excretion. 



XVIII. The Saeeuli of the Cpinoidea. 



These are peculiar organs which, in certain Crinoids, occur in great 

 numbers below the integument, principally at the edge of the food 

 grooves of the pinnul;>j, the arms, and the disc, less frequently else- 

 where (intestinal wall, mesenteries). They are globular sacs lying 

 close below the surface, but having no outer aperture, and are closel)' 

 packed with strongly refractive spherules, which, during life, are 

 colourless, but turn red after death. Close examination shows that 



