142 P. HERBERT CARPENTER. 
inserted these vessels in the figures of his vertical and trans- 
verse sections of the pharynx, without having seen something 
which he might have mistaken for vessels. But, according to 
Koehler, nothing of this kind is present; nor will anyone ever 
discover such vessels, even with the eye of faith. ‘ Les deux 
vaisseaux radiaux ne communiquent qu’avec l’un des deux 
anneaux,” that, namely, which communicates with the exterior 
through the water-tube and madreporite, and is generally 
known as the water-vascular ring. 
Unfortunately, however, Koehler’s statements upon this 
point have not been supported by any figures; and in reply to 
my remark to this effect Koehler says: “ En ce qui concerne 
les figures, je crois en avoir donné d’assez nombreuses et 
d’assez démonstratives, mais 4 propos de la circulation de 
Voursin il m’a semblé inutile de représenter 4 nouveau des 
dispositions déja figurées par Perrier.” But since the second 
radial vessel (the blood-vessel, as I regard it) was entirely 
unknown to Perrier, Koehler would have done well to give a 
figure showing its (supposed) junction with the radial water- 
vessel which was described and figured by Perrier.! Such 
a figure would go far to support Koehler’s assertion, which, 
if true, must necessitate a considerable change in the generally 
received ideas respecting the morphology of the Echinoderm 
vascular system. I presume that it would not be difficult to 
obtain a series of sections through the part where the double 
radial vessels “ become simple.” But the figure illustrating 
this point, whether of an injected preparation or of a section, 
has yet to be drawn; and we must content ourselves for the 
present with Koehler’s bare statement of the fact. 
He is surprised at my representing him as considering the 
“‘ madreporic canal ” which runs from the organ of excretion of 
Spatangus towards the madreporite as the water-tube. I 
must apologise if I have misunderstood him; but I used the 
word water-tube=Steincanal=canal du sable, as denoting the 
vessel by which the oral vascular ring that supplies the 
1 « Recherches sur l’appareil circulatoire des Oursins,” ‘ Arch. de Zool., 
Exp. et gén.,’t. iv, 1875, p. 621, pl. xxiv. 
