REPORT ON THE CRINOIDEA. 101 
in vertical sections of a disk that is moderately free from pigment. In none of the 
species of Pentacrinus or Comatula which I have examined, have I failed to observe 
this connection satisfactorily ; and in some fortunate sections the vascular structure may 
be traced right down from the oral ring into the lower and more compact portion of the 
plexiform gland (Pl. LXIL). This is generally more or less lobulated in form, and in 
this respect very striking differences exist among the various types of Crinoids. 
Both in Rhizocrinus (Pl. Villa. figs. 7, 8, x), and in Bathycrinus (Pl. VIIb. 
figs. 1, 4-8, 2) it is almost as simple as in the Pentacrinoid. It is oval-oblong in section 
and has but slightly developed irregularities of outline. In Antedon rosacea, and in the 
lower part of the disk of Pentacrinus, until it commences to subdivide, it is more irregular 
in form (Pl. LVIII. fig. 4, x); and it shows indications of its lobular structure, as is well 
seen in Ludwig's admirable illustrations ' of the former type. I have made no horizontal 
sections of the disk of Antedon eschrichti, but imagine that its plexiform gland must be 
not very unlike that of Promachocrinus kerquelensis. Figs. 5 and 6 on Pl. LVIIL represent 
horizontal sections through the gland in the lower half of the disk of this type, fig. 6 
being that nearer the calyx. The irregularity in the form of the organ is very striking. 
The upper part of the same disk was cut into vertical sections. They show the extreme 
subdivision of the ventral end of the plexiform gland, and the termination of its branches 
in the well defined labial plexus, the spongy part of which is represented in Pl. LIX. 
fig. 9, xv. 
The minute structure of the plexiform gland of the Crinoids is as yet unknown. 
According to Perrier? it is identical with that of the same organ in other Echinoderms. 
Fresh specimens, and not spirit-material, are absolutely essential for its elucidation ; but 
as Perrier and Koehler, who have both studied the plexiform gland of the Urchins, give 
accounts of its structure which differ from one another, and from Apostolidés’ description 
of the same organ in Ophiurids, there is a difficulty in determing from analogy, and 
still more so from observation, what its real nature is in Crinoids.*? Certain peculiarities 
that I have noticed in the appearance of its lower portion in Pentacrinus decorus lead 
me to think that Koehler’s account of it in the Urchins* is probably more correct than 
those of his fellow-workers. 
Upon one point, however, Iam quite satisfied. Although the condition of my material 
entirely precluded any minute observations on the structure of the plexiform gland, I 
have had no difficulty in tracing its connection with the intervisceral blood-vessels of the 
lower part of the disk (Pl. LVIL. fig. 2, Pl. LVI. fig. 6). This point was first noticed by 
Ludwig in Antedon rosacea, and he illustrated it with an excellent figure.’ I have 
1 Crinoideen, loc. cit., Taf. xviii. figs. 57-59. 
2 Sur organisation des Crinoides, Comptes rendus, t. xevii., No. 3, p. 18. 
3 For a discussion of this subject see Quart. Journ. Mier. Sci., N.S., vols. xxii—xxiv., 1882-1884. 
4 Recherches sur les Echinides des Cotes de Provence. Ann. du Mus. d’ Hist. Nat. de Marseille, t. i. pp. 73-77, 95-99. 
5 Crinoideen, loc. cit., Taf. xviii. fig. 59. 
