430 SUMMARY OP CURRENT RESEARCHES RELATING TO 



long, lying in the freo nmbulacral cliambcrlcts. In Asthenosoma they 

 arc mere cvaginations of the membrane of the lantern, and are devoid 

 of the secondary diverticula which they havo in the Cidaridffl. 



Researches on Dorocidaris papillata and other Mediterranean 

 Echinids.* — M. H. Prouho lias, inter alia, studied the development of 

 the spines of Dorocidaris papillata. He has not been able to determine 

 the functions of the glandular pedicillariro, each calcareous valve of 

 which contains a mucous sac. The principal bundles of the peripheral 

 nerve-plexus are situated in the special grooves hollowed out in tho 

 calcareous surface of the test ; this discovery explains the nature of the 

 grooves which have been observed on fossil species ; the peripheral 

 plexus forms a nerve-ring at the base of each spine, which is visible to 

 the naked eye. The ambulacral nerves are tubular, and the intra-neural 

 space ends between the efritheliuni of the pharynx and that of the peri- 

 stomial lip. The internal part of the ambulacral nerve-tubes forms tho 

 peribuccal ring, which is continuous with the epithelial layer of the 

 pharynx. In D. papillata alone, so far as is known, there is no intestinal 

 siphon to the digestive tube. The visceral lacunar system is solely 

 composed of lacuna? hollowed out in the connective tissue of the mesen- 

 teric layers ; the absorbing capillary plexus opens into two marginal 

 lacuna;, one of which is external and one internal. The internal marginal 

 lacuna leads into a peri-cesophageal ring which is placed in the internal 

 wall of the aquiferous ring. This lacunar ring gives rise to a plexus 

 which is distributed to the ovoid gland, and is continued into the genital 

 pentagon, and five pharyngeal lacuna? ; the latter give off five radial 

 lacuna?, which again give off lateral branches for the tentacles. No 

 Polian vesicles are differentiated from the oesophageal rings. Tho 

 visceral lacunar system does not communicate with the exterior; nor 

 does the ring belonging to that system communicate with the aquiferous 

 ring. 



The larval form of D. papillata is a pluteus with four pairs of arms, 

 two of which have delicate spicular networks ; the cupola is flattened, and 

 has two lateral lobes, in addition to which there are other well-developed 

 lobes along the ciliated fringe ; there are no ciliated epaulets. 



In Echinus acutus M. Prouho has discovered the peripheral nerve- 

 plexus, and a genital nerve-ring connected with the five ambulacral 

 nerves. In Strong ylocentrotus lividus the five genital glands were 

 observed to arise from a single primitive bud, which is developed at the 

 expense of the mesentery ; the ovoid gland is not a genital stolon. 

 Spatangus purpureus has an internal apophysis, at the extremity of which 

 the aquiferous tube and the annexed canal open. The internal marginal 

 lacuna gives off a branch which forms a circumoral lacunar ring ; this 

 ring gives off on one side five radial lacuna?, and on the other a lacuna 

 (glandular canal) which extends as far as the ovoid gland, is distributed 

 in its walls, and. ends in a plexus in the membrane which connects 

 together the four genital glands. The aquiferous apparatus is divided 

 into two parts which do not communicate with one another ; there is the 

 true aquiferous tube, prolonged by a ramified canal which ends in a cul- 

 de-sac near the oesophageal region, and an ambulacral system consisting 

 of five radial vessels, a circumoral ring, and a canal which extends along 



* Arch. Zool. Expe'r. et Gen., v. (1887) pp. 213-380 (13 pis.). See also this 

 Journal, 1 887, p. 400. 



