102 THE VOYAGE OF H.M.S. CHALLENGER. 
myself described and figured the same connection in Actinometra parvicirra ;* and I 
have since seen it so frequently in the different species which I have studied, that I 
read the following statement of Perrier’s with some little surprise. Speaking of the 
plexiform gland of Antedon rosacea, he says,” “ Les vaisseaux qui paraissent en partir ne 
sont autre chose que les ramifications de la glande, se terminant d’ordinaire par des ren- 
flements ayant l’aspect de culs-de-sac. Ces ramifications courent au milieu des innom- 
brables trabécules du tissue conjonctif de la cavité générale, qui peuvent eux mémes 
parfois prendre l’apparence des vaisseaux.” I cannot gather from this passage whether 
Perrier means to deny the existence of intervisceral vessels altogether, or merely the 
connection of this system with the plexiform gland. I have good reason to believe, as 
pointed out elsewhere,’ that his statements refer solely to Antedon rosacea ; but even in 
this unfavourable type I have had no difficulty in confirming Ludwig's observations 
respecting the relations of this organ to the blood-vessels. If the latter be ramifications 
of the gland, as Perrier asserts, one would expect that they should have the same structure 
as it; whereas their nature is the same as that of the intervisceral blood-vessels, which 
are lined by a layer of pavement-epithelium (PI. LVII. fig. 5); while their apparent 
blindness is simply due to the impossibility of any single section showing more than a 
very small portion of their winding course. A careful study of a good dissection, or of 
a moderately thick transparent section, especially with a binocular, or an accurate 
plotting out on paper of a series of thin sections by means of a camera, will reveal much 
that is totally unrecognisable in other ways. [See Appendix, Note E. ] 
I have studied the intervisceral blood-vessels principally in <Antedon eschrichti, 
Pentacrinus decorus, and Actinometra parvicirra. In the Pentacrinus, with its body- 
cavity reduced by the presence of much calcareous tissue, the visceral blood-vessels are 
less abundant within the simple coils of the digestive tube than on its outer surface, 
where they may be excellently seen in tangential sections of the visceral mass, as shown 
mm PL LVL. fig. 5, 2b. 
But in Antedon eschrichti and Actinometra, which have a more complex digestive tube, 
the intervisceral blood-vessels are more largely developed. The connection of one of them 
with the plexiform gland of Promachocrinus kerguelensis is shown in horizontal section 
in Pl. LVIII. fig. 6, while Pl. LVIL. fig. 2 represents a portion of one of several vertical 
sections of Pentacrinus decorus in which the same point is visible, the plexiform gland 
itself unfortunately having no recognisable structure. 
The blood-vessels may be readily distinguished from connective tissue, especially in 
Pentacrinus ; for nearly all the visceral connective tissue of this type 1s regularly calcified, 
1 The Minute Anatomy of the Brachiate Echinoderms, Quart. Journ. Micr. Sci., N.S8., vol. xxi., 1881, p. 185, pl. xii. 
ae soe rendus, t. xevii. p. 188. 
3 Notes on Echinoderm Morphology, No. VI. ; On the Anatomical Relations of the Vascular System, Quart. Journ. 
Mier. Sct., 1883, vol. xxiii. p. 610. 
