REPORT ON THE CRINOIDEA, 31 
Both in Bathycrinus and in Rhizocrinus the organic and calcareous networks, which 
interpenetrate one another, are not always perfectly continuous throughout the 
substance of the stem-jomts. For both in optical and in transverse sections of de- 
calcified stems empty spaces are often visible, especially in the immediate neighbourhood 
of the central axis. Five of these spaces appear in some of my transverse sections of 
the lower stem-joints of Bathycrinus (Pl. VIIa. fig. 2, rs). They are radially disposed, 
being situated immediately outside the five peripheral vessels of the central axis (ch’), 
which they may not greatly exceed in size. Both spaces and vessels may contain 
larger or smaller masses of pigment granules (p). The walls of the former are less 
well-defined than those of the latter, but are distinctly sharper than the outlines of 
the spaces in the organic plexus forming the remainder of the stem-joint. 
It sometimes happens in the lower part of the stem that one of these spaces may 
increase very greatly in size, and so displace the central axis from its median position ; 
or the space may approach quite near to the surface of the jot. They are much 
more irregular in the lower part of the stem than in the uppermost elongated joints, 
where they are also of larger relative size (Pl. VIIa. fig. 1, 7s); and they appear to 
communicate with one another from joint to joint, through the elongated oval opening 
of the central canal (Pl. VIla. fig. 7). But there is nothing to be seen of them in the 
discoidal joints at the upper part of the stem, which are continuously traversed by 
closely set ligamentous fibres (Pl. VIIb. fig. 1). The best preparations that I have 
been able to obtain illustrative of this point have been from the stem of Bathycrinus ; 
but I have also seen these spaces, though not so well, in Rhizocrinus. The former 
genus (or at any rate Bathycrinus aldrichianus) is remarkable for the abundance of 
delicate fibrils which may be seen proceeding outwards from the central fibrillar axis 
of the stem, the nervous nature of which is gradually coming to be recognised. Some 
of the larger of these fibrils are shown in optical section in Pl. VIIa. fig. 1, ca’. But 
a much larger number of smaller ones may be seen with a high power. They leave 
the central axis in a more or less transverse direction, and form an open plexus, im- 
mediately beneath the external surface of the stem. This is most distinctly seen over 
the radial spaces, where the decalcified stem is, of course, more transparent than else- 
where. It is noteworthy that the arms of Bathycrinus aldrichianus, like the stem, are 
also remarkable for the large number of branches which proceed outwards from their 
axial cords (Pl. Vb. figs. 6, 7; Pl. VIIa. figs. 4, 5—a’). The corresponding branches 
in the stem of Pentacrinus have been already noticed (ante, p. 23). 
C. Hyocrrmip&. 
The stem of Hyocrinus is one of considerable interest, because it is the only recent 
Crinoid in which the terminal faces of the stem-joints are of the same nature as those of 
