154 P. HERBERT CARPENTER. 
retical ones on which Koehler comments, for doubting his 
description of the communication of the two vascular systems 
of an Urchin, both with one another and with the exterior. 
But at the same time I am fully prepared to abandon my doubts 
and to admit the truth of his views, when he can demonstrate 
the following propositions by the same methods as Ludwig 
employed in his work on the Starfishes. 
1. The communication of the so-called excretory canal of 
the ovoid gland in an Urchin with the space beneath the 
madreporite, into which the pore-canals and the water-tube 
both open. 
2. The connection of both the radial vessels of an Kchinus 
with one oral ring (water-vascular, auctorum). 
3. The connection of the intestinal vessel of Spatangus 
with both the oral rings. 
In these days of an intensely elaborated technique and self- 
acting microtomes, it must surely be possible to obtain such a 
series of sections as would put the truth of Koehler’s views 
beyond the reach of doubt; but if obtained they have not yet 
been figured. We are indebted to him for the rediscovery of 
the “ glandular canal” of Echinus, by which the ovoid gland 
communicates with an oral blood-vascular ring. This con- 
nection was positively denied by Perrier,! as the result of 
unsuccessful injections. Koehler’s injections were more for- 
tunate, however, and he confirmed his results by making 
tranverse sections of the combined water-tube and glandular 
canal,? which place his discovery upon a sure foundation. Can 
he not do the same for the three anatomical points mentioned 
above ? 
I trust that what I have written above will not be considered 
as wanting in courtesy to Mons. Koehler. Weowe him such a 
heavy debt of gratitude for the advance which he has made in 
our knowledge of the Echinoid vascular system, that it seems 
almost ungracious to ask for further information. His des- 
criptions of the radial blood-vessels, and of the glandular canal 
1 Arch. de Zool. Exp. et Gén.,’ t. iv, p. 613. 
? * Recherches,’ pl. vi, fig. 40. 
