MORPHOLOGICAL PART. 45 
In the Cyathocrinidw the structure at the lower part of the stem is only 
known in Barycrinus. In Cyathoerinus we have examined the stem to a 
length of 10 cm., and in Parisocrinus to about 18 cm., without finding any 
traces of lateral cirri. Neither have these been observed, so far as we know, 
among the Anomalocrinide or Hybocrinide ; but in Homocrinus scopurius 
they occur at the lower half of the stem. 
The stem of Barycrinus is quinque-partite, and enlarges gradually to the 
root, where its diameter in extreme cases reaches from 30 to 40 mm. The 
root consists of five main rami, which branch into smalier ones, so located 
that the longitudinal sutures of the stem bisect the rootlets, and the large 
central canal, which is sharply pentangular in the stem, becomes elliptic or 
linear within the branches; the latter is also the case in Ancyrocrinus, of 
which we shall speak presently. 
The axial canal is central, and extends to the full length of the stem, 
giving off branches to the cirri. The main canal is circular, angular, or pen- 
talobate ; that of the branches sometimes elliptic, the long diameter vertical. 
If pentangular, the angles are directed radially in dicyclic Crinoids, and 
interradially in monocyclic, thus alternating with the projecting angles of 
the stem joints. To this rule, however, there are two exceptions, and, so far 
as we know, only two. In Pentacrinus,and the monocyclic Glyptocrinus Forn- 
shelli'S. A. Miller, the axial canal has the same orientation as the outer angles 
of the stem. This is very remarkable, and we shall consider it further in 
discussing the basals and infrabasals. The canal in some species is quite 
minute, in others very wide; while in still others the central canal is sur- 
rounded by three, four, or five peripheral canals, as in the case of Cupresso- 
criuus, in Which pentamerous symmetry in the stem is the exception. 
In recent Crinoids the innermost part of the central canal is the internal 
vascular axis, and consists of five peripheral vessels arranged around a cen- 
tral one. The former are downward extensions from the chambers of the 
quinquelocular organ at the base of the calyx, which are connected with the 
axial vessel of the chambered organ. Whether such vessels also existed 
in the stem of Paleozoic Crinoids, of course cannot be ascertained from 
the fossil; but that a quinquelocular organ, with upward extensions to 
the arms, was present in some of them, is indicated by the structure of 
Eupachycrinus, Catillocrinus, and Agassizocrinus, where the inner floor of the 
basals and radials is apparently perforated. Carpenter* thinks it probable 
* Journal of Anatomy and Physiology, Vol. XII., p. 44. 
