REPORT ON THE CRINOIDEA, d 415 
This seems to indicate clearly that the interarticular fibres of the cirri are muscular 
in function, though not striated like the ventral fibres which unite the arm-joints, and 
have hitherto been regarded as the only true muscles of the Crinoid organisation. 
Four years ago I pointed out that the appearance of some of my sections had led me 
to think that the axial cord of the arm consisted of two lateral fibrillar masses enclosing 
a central structure." According to Jickeli? this last is a longitudinal septum between 
two tubes which contain blood-corpuscles; while the whole structure is enclosed in 
a sheath of nervous tissue. Within the calyx the tubes of the different rays unite 
laterally and “gehen durch eben solche das gekammerte Organ theilweise bedeckende 
Fortsitze in ein spongidses Geflecht tiber, welches dem gekammerten Organ wie eine 
Kiippe aufsitzt. Von diesem spongidsen Geflecht entspringen die Fortsetzungen in die 
Cirrhen. Die Wandung dieses Réhrensystems ist die nervése Substanz, die Masse, 
welche dasselbe erfiillt, besteht aus geronnenem Plasma, in welches Blutzellen einge- 
backen sind.” It does not appear, however, that these axial blood-tubes are in any 
way connected with the cavities of the chambered organ. Jickeli poimts out that 
his observations confirm the statements of Miiller? respecting the presence of a blood- 
vessel within the central canal of the arms, which subsequent workers have generally 
considered to be erroneous. He finds that the elements of the nerve sheath surrounding 
these blood-vessels are most easily demonstrated in the radial axillaries where the axial 
cords of two arms unite, and he describes the presence of ganglionic cells with from two to 
six processes, some of which unite with those of other cells, He has also seen the 
muscular branches of the axial cords, the existence of which, according to Weinberg, is 
only a supposition ; and by the use of polarised light he has traced these into the dorsal 
as well as into the ventral musculature. 
He doubts the presence of a definite oral ring in the ambulacral nervous system. 
For he finds that the ventral nerves extend down into the fore-gut beneath its 
epithelium, which is directly continuous with that lining the food-grooves. The appear- 
ance of several of my sections, both of Pentacrinus and of Comatula, has led me to 
suspect this fact; but I have hesitated to say so, as I wished to verify it by making 
some sections of individuals which had been properly prepared for histological work. 
This having been done by Jickeli, I am glad to be able to confirm his observations. 
He believes himself to have discovered yet another nervous structure in the Crinoid 
organisation, “es ist noch ein drittes bis dahin nicht bekanntes, im Bindegewebe gelagertes 
Nervencentrum vorhanden, welches die Mundéffnung umgibt, und die radialen Wasser- 
gefiisse jederseits als ein gesonderter, an die Tentakeln in regelmissigen Abstiinden 
Zweige abgebender Strang begleitet.”* The peripheral parts of this system appear to me 
to belong to what I have called the parambulacral network, situated in the ventral 
* Quart. Journ. Mier. Sci., 1881, vol. xxii., N. S., p. 187. 2 Zool. Anzeiger, vol. vii. p. 368, 1884. 
§ Bau der Pentacrinus, loc. cit., p. 22. 4 Zool. Anzeiger, vol, vii. p. 370, 1884. 
