372 p. HERBERT CARPENTER. 



part of the blood-vascular system at all, but an excretory gland. 

 It is said (though not by Jourdain) to communicate with the 

 exterior through the madreporite, instead of joining an aboral 

 ring, as described by Ludwig; while it has no connection with 

 any blood-vascular ring situated between the nervous and water- 

 vascular rings. Neither are there any radial blood-vessels other 

 than the subdivisions of the body cavity, which have been 

 variously termed " nerve-vessels'' or "perihsemal canals/' &c. 



Ludwig has not yet published any of his observations on the 

 anatomy of the Urchins ; and it will be interesting to compare 

 his results with those of Peirier and Koehler. In the case of 

 the Ophiurids, however, we have the elaborate work of Aposto- 

 lides^ to contrast with those of his German predecessors. He 

 was fortunate in having had an abundant supply of living 

 specimens at his disposal, while Ludwig dealt exclusively with 

 spirit material ; but the differences between their results are too 

 great to be ex})Iained by this circumstance alone. 



The so-called " Herz " or " Herzgeflecht " of the Ophiurids 

 is termed the " piriform gland " by Apostolides ; and he says 

 (p. 147) that after the removal of the common envelope of this 

 organ and of the water-tube, " II est impossible de ne pas voir 

 la communication directe de la glande piriforme avec I'exterieur.^' 

 He gives a good figure illustrating this point, which it is in- 

 teresting to compare with that given by Perrier^ of the internal 

 relations of the madreporite in an Urchin ; and like Perrier, he 

 finds his observations to be confirmed by the results of injec- 

 tions. Both authors assert positively that the other end of the 

 piriform gland is entirely free, no vessel proceeding from it to 

 join an oral ring. Both, and also Koehler, describe it as having 

 a central cavity with a series of radiating cellular columns or 

 acini disposed around it, points which can only be made out in 

 fresh specimens. 



In the face of these detailed observations made on fresh 

 material it is difficult to avoid the suspicion that the so-called 

 central plexus of the Echinozoa may after all be of a glandular 

 nature, and unconnected with the vascular system, though on 

 the other hand, it is quite possible that its connection with an 

 oral ring may have been overlooked by the French naturalists. 

 Many of their observations, and especially those of Jourdain, 

 confirm the statements of Ludwig, which are, however, totally 

 ignored by the French author. 



' " Anatomie et Developpement des Opbiures," ' Arch, de Zool. exple. 

 et jrenerale,' vol. x, pp. 121-224. 



^ " Recherclies sur I'Appareil circulatoire des Oursins," 'Arch, de Zool. 

 exple. et genie.,' vol. iv, pi. xxiii, fig. 1. 



