1 6 Echinoderma. 



appear in the wall of the stone-canal when but 7 median dorsals are formed, and 

 before there is any cribriform plate over its opening. 



Jickeli finds that in the ambulacral nerve ring of Asterias rubens dorsal and 

 ventral fibre-masses may be distinguished, and in Stichaster roseus this distinction 

 extends through the whole ambulacral nerve. Other radial nerves occupy the 

 intervals between the rows of calcareous plates on the arm, with connecting fibres 

 between them. They form a subepithelial plexus and are very distinct in Astrogo- 

 nium granular e. Lange's nerves are masses of ganglion cells with uniting fibres 

 which lie beneath the epithelium of the radial blood-sinus and are separated by a 

 layer of connective tissue from the ambulacral nerves. A layer of nerve fibres 

 and stellate cells occurs at the base of the epithelium throughout the digestive tube . 



Durham (*) notes that minute foreign bodies introduced into the coelom of a 

 Starfish are removed to the exterior by the contained phagocytes which pass 

 out through the walls of the papulae. The large corpuscles with refringent gra- 

 nules (plasma- wandercells) also migrate to the exterior in the same way. Dur- 

 ham ( 2 ) further points out that some of the pore-canals in the madreporite of 

 Cribrella ocellata open into the axial sinus, which likewise communicates with one 

 of the lateral lobes of the ampulla at the top of the water-tube. 



Griffiths has detected uric acid in the secretion of the 5 gastric pouches of 

 Asterias rubens. 



Semon points out that the second or pre-oral ciliated b and of Asterid larvae 

 is merely an outgrowth from the adoral band , with which it remains connected 

 throughout the Brachiolaria-stage. 



Perrier notes that in Labidiaster radiosus new arms are formed after the close 

 of the larval period. They are budded off from the edge of the disc, behind the 

 dentary pieces of the existing arms , so that their ambulacra do not reach the 

 buccal membrane. 



IV. Ophiuroidea. 



See also Fewkes, supra, p 15, Neumayr. supra, p 5, and Semon, supra, p 3. 



Cuenot ( 2 ) has studied the minute anatomy of the Ophiurids and Euryalids. 

 The coelom and vascular sinuses of the latter are lined throughout by epithe- 

 lium, as in 'the Asterids, but in the Ophiurids the mesenteries and genital glands 

 only bear scattered nuclei , and an epithelium . though present in the general 

 cavity of the arm, is absent in the vascular sinuses ; while the external epithelium 

 only occurs at the bases of the spines, on the tube-feet etc., being reduced else- 

 where to a mere nuclear layer. In the Euryalids, however, the disc and arm 

 bases are covered with a relatively high epithelium. The arms of species 

 living on a rocky bottom or one with abundant vegetation bear, in addition to the 

 spines, numerous minute hooks clothed in perisome, with the handle end adoral 

 and the curved part aboral. They do not occur on the spineless arms of species 

 living on a sandy bottom. -- The glandular cells lining the digestive tube are 

 similar to those found in the Asterids [supra p 12], high, filled with coloured 

 digestive granules, and covered by a thick and ciliated cuticular plate ; but there 

 is no nervous layer between the bases of these digestive cells. In the Ophiurids 

 the wall of the fore-gut is continuous with the nerve ring, but only by means of a 

 thin prolongation of the latter on which its epithelionervous layer is extremely 

 reduced, no nerve fibrils being traceable. In the Euryalids, however, the di- 

 gestive epithelium has no relation with that of the nerve ring , but is continuous 

 with the external epithelium , more especially that of the dentary pieces ; while 

 the nerve ring gives off numerous branches which form a complex network in the 



