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-joints. 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 (PI. Vila. 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 joint. 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 Vila. fig. 1, rs) ; 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 Vllb. fig. ] ). 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 Vila. 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 numl)er of branches which proceed outwards from their 

 axial cords (PL Vllb. figs. 6, 7 ; PL Villa, figs. 4, 5 — a'). The corresponding branches 

 in the stem of Pentacrinus have been akeady noticed {a^ite, p. 23). 



C. Hyocrikid^. 



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 



