NOTES ON ECHINODERM MORPHOLOGY. 601 



with those of other workers, especially Teuscher and Ludwig, 

 both in this group and in other Echinoderras. He entirely 

 ignores the fact that blood- vascular and water-vascular systems, 

 consisting respectively of oral rings and radial vessels, have 

 been described as distinct and totally independent in Asterids, 

 Ophiurids, and Crinoids, apart from Teuscher's work on the 

 Urchins. He continually speaks of the ambulacral vessels as 

 being " double," meaning that both of them belong to what 

 Perrier called the respiratory portion of the vascular system, 

 that, namely, which communicates with the exterior by the 

 water-tube. The so-called absorbent portion of the vascular 

 system consists of the intestinal vessels, the ventral one of which 

 is connected with the superior oral ring. 



Koehler's position, therefore, involves the curious anomaly 

 that Echinus has two oral rings, both containing blood, but 

 the one is "absorbent" and the other "respiratory;" while 

 there are also two sets of radial vessels, both, however, belong- 

 ing to the respiratory system, and connected exclusively with 

 one ring (water- vascular, auct); whereas in Spatangus, as 

 he himself describes, each oral ring is connected with a cor- 

 responding set of radial vessels. This is also the case in all 

 the other Echinoderms ; and I cannot but think that the great 

 difficulties involved by the presence of the lantern in Echinus 

 may have caused the connection of the smaller radial vessels 

 with the superior oral ring to have escaped Mons. Koehler's 

 notice. He gives no figure showing their union with the 

 water-vessels proper before joining the inferior or water- 

 vascular ring, which suggests the possibility that the supposed 

 union is an inference and not an observed fact. But if an 

 inference was necessary, it would surely have been more natural 

 to suppose that a character which has been described by four 

 different observers in Asterids, Ophiurids, Crinoids, and 

 Spatangids, is also to be found in Echinus. 



The next point to be considered is the connection of the so- 

 called heart or ovoid gland with the vascular system, which 

 has been so positively denied by Perrier. The glandular canal 

 discovered by Koehler which rises from the superior oral ring 



