12 Echinoderina. 



derm contains unicellular mucous glands and also large muriform cells containing 

 yellow granules, which are defensive organs like nematocysts. They are most 

 abundant in Astropecten and Echinaster; the pigment of these types occurs as 

 small granules in the ectoderm cells. E. sepositus has dermal glands, the cell pro- 

 toplasm of which becomes transformed into yellow vesicles, similar to the granules 

 of the muriform cells. The lacunar spaces in the walls of the papulae are 

 closed, and not in communication with the schizocoel-spaces of the body wall as 

 supposed by Hamann ; while the cells lining them are not epithelial but merely 

 the embryonic cells of the connective tissue. The ends of the papulae in Luidia 

 ciliaris are not simple, but form a bunch of small caeca; and the marginal plates 

 bear minute spines covered with long cilia which produce currents from the ventral 

 towards the dorsal surface. Similar vibratile radicles occur in Astropecten. The 

 characters of the pedicellariae vary greatly in individuals from different loca- 

 lities, and no sharp distinction can be drawn between them and spines, transition 

 forms being abundant. Tridactyle pedicellariae, like those of Luidia, occur in 

 some forms of Asterias glacialis. Forcipi formes and forficiformes are 

 similar in their earliest developmental stages, and the former represent the per- 

 fected form of the latter. The pedicellariae are defensive organs, serving to pro- 

 tect the papulae and tube-feet by grasping foreign bodies which can then be sur- 

 rounded by mucus and attacked by the vesicles ejected from the muriform cells 

 of the ectoderm. In Astropecten this defensive function is performed by the paxillae, 

 and in Echinaster by the dermal glands. In all Asterids, and especially in the 

 Echinasteridae, the beginning and end of the stomachic sac are rather more 

 glandular than the intermediate part. E. sepositus and Cribrella oculata have 10 

 glandular pouches connected with the gullet, while the rectal caeca are bilobed 

 with villous walls. They are absent in Luidia and vary greatly in development 

 in other Asterids. The flask-shaped unicellular glands described by Hamann [see 

 Bericht for 1885 I p 189] in the mid-gut are non-existent; but the epithelium 

 contains cup-shaped mucous cells, each supported on a nucleated stem. They are 

 ciliated, but without a cuticular plate and contain a clear reticulum. The more 

 numerous granular cells which are also ciliated and have cuticular plates are 

 much elongated and contain a protoplasmic reticulum in which refractile granules 

 are formed, to be ultimately discharged. Bipolar cells occur among the delicate 

 nerve fibrils which lie between the bases of the filamentous cells forming the 

 ambulacral epithelium, but there are no others. The nerve band is continued 

 down from the peribuccal ring into the glandular wall of the digestive tube, even 

 extending into the oesophageal pouches of the Echinasteridae. It occurs all through 

 the stomach, gradually diminishing in thickness and enters both radial and rectal 

 caeca. The entire epidermis contains a superficial nerve plexus, which is somewhat 

 thickened in the papulae and pedicellariae ; it is directly continuous with the nerve- 

 band in the ambulacral epithelium. The latter gives off no branches to the muscles, 

 nor are its fibrils continuous with any special sensory cells, as supposed by Hamann ; 

 for the lower end of each epithelial cell rests upon the subjacent connective tissue. 

 A certain number of tube-feet towards the end of the arm are elongated and 

 without suckers, being specially modified for tactile purposes. The eye-spot 

 contains a number of small pigmented cups which are lined by modified epithelial 

 cells with their upper ends enlarged and full of pigment granules. They bear 

 cuticular plates, but no cilia, and their filamentous bases terminate in slight swell- 

 ings upon the subjacent connective tissue. The nerve band is less thick in the 

 eye-spot than in the rest of the radial cord. The latter is a coordinating centre 

 for the movements of the tube-feet in its own arm ; while the oral ring coordinates 

 the movements of the arms inter se. Stimulation of the pedicellariae on a piece 



