NOTES ON ECHINODERM MORPHOLOGY. 149 
animals, with whose morphology he may make himself thor- 
oughly acquainted. This method depends upon the very 
general assumption that the other members of the group of 
animals to which each type form belongs will resemble it in 
all those essential characters by which it differs from the other 
types. Next to the radial symmetry and the peculiarities of 
the skeleton, there is, I take it, no feature which is so emi- 
nently characteristic of Echinoderms as the presence of two 
sets of radial vessels, the water-vessels and the blood-vessels of 
authors ; and of two corresponding vascular rings, the one 
communicating with the exterior through the stone-canal, and 
the other connected with the cavities of the remarkable glan- 
dular organ which was formerly considered as a heart. 
Now the most careful observations which have yet been 
made upon the Starfish (the typical Echinoderm of every 
teacher) go to show, not only that the so-called water-vascular 
and blood-vascular systems are fundamentally independent of 
one another, but also that the latter does not communicate 
with the exterior through the madreporite, as the former does ; 
and I have a strong conviction that equally careful observa- 
tions, conducted by the same rigorous methods, will show 
that these characters exist in the Urchins. They have been 
described as presenting themselves in Ophiurids and in Cri- 
noids. But although the accuracy of these descriptions has 
been called in question by the French zoologists, no proof has 
yet been furnished that they areincorrect. Thus, for example, 
Ludwig describes the single water-pore of Ophiurids as leading 
(directly or indirectly) into the stone-canal; while the so- 
called heart “endigt iiber der Innenseite der Madreporenplatte 
neben der Stelle, an welcher sich der Steinkanal mit der 
Madreporenplatte verbindet.!. He figures some selected hori- 
zontal sections through the madreporite, which, as usual, fully 
bear out his statements. 
Then comes Apostolidés’? who tells us how “ Chez les 
1 “Neue Beitrage zur Anatomie der Ophiuren,” ‘ Zeitschr. f. wiss. Zool., 
Bd. xxxiv, 1880, p. 351. Taf. xiv, figs. 1—3. 
2 « Anatomie et Developpement des Ophiures,” ‘Arch. de Zool. exp. et 
Gén.,’ vol. x, 1881, p. 25 (of separate copy). 
