REPORT ON THE CRINOIDEA. 415 



This seems to indicate clearly that the iuterarticular fibres of the cirri are muscular 

 iu 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 

 Fortsatze in ein spongioses Geflecht liber, welches dem gekammerten Organ wie eine 

 Kappe aufsitzt. Von diesem spongiosen Geflecht entspringen die Fortsetzungen in die 

 Cirrhen. Die Wandung dieses Eohrensystems ist die nervose Substanz, die Masse, 

 welche dasselbe erfiillt, besteht aus geronnenem Plasma, in welches Blutzellen einge- 

 baeken sind." It does not appear, however, that these axial blood-tul)es are in any 

 way connected wdth the cavities of the chambered organ. Jickeli points out that 

 his observations confirm the statements of Miiller ^ respecting the presence of a Ijlood- 

 vessel within the central canal of the arms, which subsec[uent 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 amljulaeral 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 eindrittes bis dahin nicht bekanntes, im Bindegewebe gelagertes 

 Nervencentrum vorhanden, welches die Mundoffnung umgibt, und die radialen Wasser- 

 gefasse jederseits als ein gesonderter, an die Tentakeln in regelmassigen Abstanden 

 Zweige abgebender Strang begleitet."* The peripheral parts of this system appear to me 

 to belong to what I have called the parambulacral network, situated iu the ventral 



1 Quart. Journ. Micr. Sci., 1881, vol. xxii., N. S.. p. 187. ^ Zool. Aimiger, vol. vii. p. 368, 1884. 



' Bail der Pentacrinus, foe. cit, p. 22. * Zool. Anzeiger, vol. vii. p. 370, 1884. 



