NOTES ON ECHINODERM MORPHOLOGY. 151 
former is less satisfactory, when used singly, than the latter ; 
and that its results require to be checked by a careful 
anatomical investigation before they can be trusted too im- 
plicitly. 
I am well aware of the danger of placing too much reliance 
upon a theoretical morphology of Echinoderms: and I have so 
often alluded to it in discussing the nervous system of Crinoids! 
that I am not surprised to be told that my doubts as to the 
accuracy of the French observations respecting the communi- 
cation of the ovoid gland of an Urchin (or Ophiurid) with the 
exterior are due to the influence of preconceived theoretical 
ideas. But, all the same, I find it difficult to believe that there 
should be such a difference between the vascular systems of 
Urchins and Starfishes respectively as is revealed by a compari- 
son of the results of Perrier and Koehler on the one hand, and 
of Ludwig on the other. . 
The statements of the French authors are based upon the 
results of injections. So were the assertions of Hoffmann, 
Greeff, and Teuscher respecting the communication of some of 
the pores in the madreporite of a Starfish with the tubular 
space which surrounds both the ovoid gland and the stone- 
canal. Ludwig, however, working with four different species, 
made sections of the madreporite in three different planes, and 
dissected out its surroundings under a lens: “In allen Fallen 
war das Resultat dasselbe. Nicht eines der Porencanilchen 
fihrt wo anders hin als in den Steincanal (oder dessen 
nachher zu besprechende ampullenformige Erweiterung); das 
gesammte Canalsystem der Madreporenplatte steht 
einzig und alleinin Zusammenhang mit dem Stein- 
canal, aber nicht mit dem schlauchformigen Canal, noch 
auch mit irgend einem anderen Hohlraum.’’? 
This very definite statement has never been contradicted, 
even by Messrs. Perrier and Poirier, who while asserting 
1 The present position of this question has been described by a distin- 
guished biologist as “ the triamph of physiology over morphology.” 
2 “ Beitrage zur Anatomie der Asteriden,” ‘ Zeitschr. f. wiss. Zool.,’ Bd. 
xxx, 1878, p. 104. 
