NOTES ON ECHIxVODERM MORPHOLOGY. 373 



According to Messrs. Perrier and Poirier/ "Ce que Ton 

 persiste encore a designer, dans nombre d'ouvrages, comme le 

 coeur chez les Bchinodermes, n'est done, chez tons les anitnaux 

 de cet embranchement, qu'un simple corps glandulaire." I shall 

 be greatly interested in learning the results to which these 

 authors are led by their investigation of the central plexus of the 

 Criuoids. I have studied its connection with the iutervisceral 

 blood-vessels in Antedon, Actinometra, Bathycrinus, and Hyo- 

 crhms. Its connection with the chambered organ below and 

 with the oral blood-vascular ring above -are not difficult to make 

 out, and though its walls are glandular it has no communication!^ 

 with the exterior. Should the views of the Prench school re- 

 specting the "piriform gland '^ of the Echinozoa be really 

 correct, there must be more difference between these animals 

 and the Crinoids than we have suspected of late years. 



With respect to the radial blood-vessels of the Ophiurids, 

 however, I have little doubt that Apostolides is entirely in the 

 wrong, and that he has altogether failed to see them, although 

 they have been figured by Simroth, Lange, Teuscher, and 

 Ludwig in longitudinal and transverse sections of the arms of 

 seven different species.^ Apostolides has partially confounded 

 the radial blood-vessel with the perihsemal space above it (nerve- 

 vessel, anc{)f although he was acquainted with Ludwig^s works, 

 in which the two are clearly distinguished. He redescribes this 

 last under the name of the " radial space,'' and considers it as a 

 part of a vascular system, "compose d'une serie de lacunes, 

 existant entre les differents organes, systeme completement clos et 

 ne communiquant nullement avec Pexterieur.'' In reahty, how- 

 ever, the whole of this system is the reduced body cavity sub- 

 divided into various portions, somewhat as it is in the arms of 

 the Crinoids ; and the small radial blood-vessel situated imme- 

 diately on the dorsal side of the nerve has been overlooked or 

 misinterpreted by Apostolides, who attempts to show that the 

 German authors have confounded it with the water-vessel, 

 though the two are separated by the whole height of the peri- 

 hsemal canal, radial space, or nerve-vessel. 



Thus, then, I cannot but regard the existence of radial blood- 

 vessels in Ophiurids as a well-established fact, and they must 

 certainly be connected by an oral ring, as are the water-vessels 



• " Sur I'Appareil circulatoire des Etoiles de mer.," ' Comptes Rendus,' 

 March 6th, 1882, t. xciv, pp. 658-660. 



• Judging from the meagre descriptions without figures, which have been 

 pubhshed by Jourdain, Messrs. Perrier and Poirier, I strongly suspect that 

 the real blood-vessels which have been seen and drawn by their German 

 colleagues have escaped their notice. 



