REPORT ON THE CRINOIDEA. 115 
Pl. LX. fig. 2—a.d.; fig. 6,a’. Figs. 4,5, 7, a’; fig. 8, a.d.), where muscle fibres are absent, 
indicates that if it be nervous, it must be not only of a motor but also of a sensory nature. 
This conclusion also follows from the fact that stimulation of one of the oral pinnules of 
Antedon rosacea causes the flexion of all the ten arms. This result is not simply due to 
general irritability ; for if so, it would follow when any pinnule was stimulated ; whereas 
stimulation of one of the ordinary pinnules is only followed by flexion of the arm which 
bears it. This experiment therefore is evidence of a reflex action of a somewhat complex 
nature ; and the axial cords must be the paths of both afferent and efferent impulses. 
For there is no ambulacral nerve in these oral pinnules, which resemble those on the 
hinder arms of Actinometra (Pl. LVI. fig. 7; Pl. LXI. fig. 3) in being ungrooved, and 
devoid of tentacles, blood-vessels, and ventral nerve (fig. 4). The latter is normally 
connected with the tentacles, and possibly also with a general subepidermic plexus ; 
but it has nothing whatever to do with the bodily movements of the animal, though 
perhaps influencing those of the tentacles and of the marginal leaflets or covering plates. 
Here then we have evidence in the Crinoid of a mesodermic nervous system analogous 
to that which has been discovered of late years in the Cclenterates, Worms, and 
Cheetognatha. As regards the latter group, O. Hertwig is inclined to think that “bei 
den Chetognathen sensibles und motorisches Nervensystem von einander vollstindig 
gesondert sein, ersteres wiire ektodermal, letzteres gleich den Muskeln mesodermal.” + 
Considering that nervous tissues are well developed in the mesoderm of Ccelenterates, 
one would certainly expect to find them in that of Echinoderms. The nervous system of 
a Holothurian only remains in connection with the epidermis at the distal ends of the 
entacles and tube-feet ; while the radial nerves of Ophiurids and Urchins are separated 
from the exterior by limestone plates, though coming into connection with the epidermis 
on the tube-feet. Besides the subepidermic plexus on the outside of the shell of an 
Urchin which sends fibrils to the muscles of the pedicellariz, there is another which is 
formed by filaments that are given off from the lateral branches of the radial nerves, the 
connection of which with the subepidermic plexus has not been definitely traced. 
Romanes and Ewart have further discovered that the general co-ordination of the spines 
for the purpose of locomotion depends on the integrity of an internal nervous plexus 
which is “everywhere in intimate connection with the external, apparently through the 
calcareous substance of the shell.” 
There is, therefore, no very great difficulty involved in the belief that a mesodermic 
nervous system is present in the Crinoids, The morphological difficulties resulting from its 
anti-ambulacral position are, however, considerable. But they are of precisely the same 
character as we have to face, when describing the chambered organ and the vascular axis 
of the stem as a part of the circulatory system of a Crinoid. Ludwig appears to have 
? Die Chetognathen, Jenaische Zeitschr., Bd. xiv. p. 284. 
2 Plul. Trans., 1881, p. 874. 
