MINUTE ANATOMY OF THE BRACHIATE ECHINODERMS, 191 
the arms and pinnules. I quite believe that this is part of 
their function, but if it be the whole, why do they give 
off such regular branches, the terminations of which are 
altogether outside the skeleton? Ludwig does not attempt 
to explain this difficulty. 
It is true that no connection has been actually traced 
between the fibrils of the branches of these axial cords and 
the individual muscular fibres. But how rarely has this 
connection been seen in any Invertebrate. No one has vet 
demonstrated a direct connection between the muscle-fibres 
of the Ophiurids and the nerves proceeding to them; while 
there is no more evidence for the nervous character of the 
ambulacral nerves of the Asterids than for that of the axial 
cords of the Crinoids. In fact, in one respect, there is less, 
for the ambulacral nerves of the Starfishes, like those of the 
Crinoids, give off no muscle branches whatever. But it 
must be remembered that the movements of a Starfish are 
far more sluggish than those of a Crinoid, and the number 
of muscles called into play to effect the movements very con- 
siderably less; while the influence of the axial cords upon 
the muscular contractions of the Crinoids is undoubted. 
The chief argument against the nervous nature of these 
cords is the morphological difficulty inseparable from this 
view of them. Another objection to it is the presence of the 
fibrillar sheath around the vessels of the cirrhi, and in the 
stalked Crinoids around the central vascular axis of the 
stem (19, 20),in which there are no muscular bundles. 
Dr. Carpenter’s position, however, despite this assault upon 
it, seems to me a stronger one than that held by those who 
do not question the experimental evidence detailed above, 
but decline to accept the conclusions which, in any other 
case, would naturally be deduced from it. 
The morphological difficulty accompanying Dr. Carpen- 
ter’s view is another question altogether. It is not so very 
much greater than that involved by the existence of the 
chambered organ and its connections at the dorsal end of 
the central plexus of the blood-vascular system. The repre- 
sentative of this organ in the other Echinoderms ends quite 
simply without even the most imperfect indication of any 
such structures in connection with it. Both structurally 
and as regards its dual function the whole of this apparatus 
is without a parallel in the other Echinoderms, and there is 
no place for it in the “archetype” of the group as at 
present conceived, which is simply that of the Urchins and 
Starfishes. 
Recent work on the Crinoids has shown that in some 
