598 P. HERBERT CARPENTER. 



This question of the communication or independence of the 

 water-vascular and blood-vascular systems is one of funda- 

 mental importance in the morphology of the Urchins, and 

 indeed of all Echinoderms. Hoffmann, Agassiz, and Perrier 

 have expressed their belief in the former ; while the more 

 recent work of Teuscher and Koehler seems to indicate that 

 the water-vascular and blood-vascular systems of the regular 

 Urchins, at any rate, have no communication with one 

 another, except through the spongy tissue of the Polian 

 vesicles. 



I have pointed out in previous notes ^ that Lud wig's obser- 

 vations upon the Stellerids led him to regard the so-called 

 heart as a plexiform portion of the vascular system, connected 

 both with an oral and with an aboral blood- vascular ring, the 

 former giving rise to radial trunks which lie between the water- 

 vessels and the ambulacral nerves. I have, as I have said 

 before, considerable faith in the accuracy of Ludwig's observa- 

 tions ; and this led me to suggest the possibility that the 

 connection of the "heart" or "central plexus" with a second 

 oral ring, other than that of the water-vascular system, might 

 have been overlooked by the French naturalists. I little 

 thought, however, that, as regards the Urchins, a few months 

 would bring a striking confirmation of this suggestion in the 

 complete work of Mons. Koehler himself, from whose earlier 

 writings, unaccompanied by figures, it was difficult to gain a 

 clear conception of his results. 



He has recently published an elaborate memoir,^ enriched 

 with seven beautifully executed plates, which illustrate the 

 minute anatomy of the Urchins in a manner that has never 

 before been attempted. Working, like Hoffmann and Perrier, 

 by the injection-method, he has been able largely to extend 

 the results of his predecessoi'S ; and he has also added very 

 considerably to our histological knowledge. His observations 

 have not been limited to the regular Urchins, but have been 



1 This Journal, vol. xxi, 1881, pp. 170—180 ; vol. xxii, 1882, pp. 372—375. 

 - ■' Jionlierclics .stir Ics Ecliiiiidcs dcs Cotes dc Provence," 'Ann. dii Mus. 

 dMlisl. Naf. de Marseille,' Znologio. Memoirc No. 3, pp. 1 — 107, pi. i — vii. 



