REPORT ON THE CRINOIDEA. 119 



that tliey have all the appearance of being true nerves.^ He further describes how their 

 ultimate subdivisions " aboutissent h, dcs cellules ^toil^es, dont chacune sc prolonge en 

 un fibre musculaire. Des ramifications de ce genre sont egalement en rapport avec les 

 fibres que contiennent les tentacules ambulacraires et dont un grande nombre so tiennent 

 dans les papilles sensitives de ces tentacules que Ludwig considere h. tort comme creuses." 

 Elsewhere he states that the cords are invested with a sheath of stellate cells which are 

 themselves related to connective-tissue corpuscles, and through these with the ectodermal 

 cells of the arm. These statements of Perrier's are of consideruljle importance, and 

 should his observations be confirmed the nervous nature of the axial cords will, I think, 

 be at last admitted, even by those whose scheme of Echinoderm morphology is founded 

 upon the archetype of a Stellerid or Urchin. These, however, arc formed almost entirely 

 upon the left larval antimer, whereas the chambered organ of a Crinoid and its downward 

 extension into the stem are formed in the right peritoneal tube. (See Appendix, Note G.) 



The branches from the axial cords of the rays and arms, to which allusion has so 

 frequently been made, vary considerably in their development and distribution. Among all 

 the numerous Crinoids, stalked and free, that I have examined, Rhizocrinus is the only one 

 in which these branches have not been visible. I see no reason to doubt their existence, 

 however ; but the genus is one of small size, and is also permanently fixed through life, so 

 that one would not expect to find large muscular branches proceeding from the axial 

 cords, as in the Comatulse and Pentacrinidse which are free or semi-free, and can use their 

 arms for the purpose of swimming ; whereas, according to Agassiz,^ the movements of 

 extension and fiexion of Rhizocrinus are but slow and gradual. The branches are also 

 poorly developed in the massive and sessile Holopus. But in Bathycrinus, in the 

 Pentacrinidse, and in the Comatulas they are very largely developed, occurring not only 

 in the arms and rays but also in the stem and cirri. They vary considerably in their 

 extent, some portions of the stem showing them al)undantly( PL XXIV. fig. 2, ca'), 

 while in others they are less numerous. An optical section of two decalcified stem-joints 

 oi Bathycrinus aldrichianus is shown in PL Vila. fig. 1. The larger branches of the 

 axial cord {ca') are seen with a low power where the radial spaces render the stem- 

 substance more transparent than elsewhere, Init this gives no idea of the minuteness and 

 complexity of their subdivision, which only reveals itself by the use of a high power. 



In Pentacrinus wynille-thonisoni again I have found these branches to be abundantly 

 developed in some stem-joints and almost entirely absent in others (PL XXIV. figs. 1-5). 

 The fibrillar envelope surrounding the vascular axis is sometimes in immediate contact 

 with the reticular tissue which forms the organic basis of the skeleton (figs. 2, 3). But 

 in other joints it is closely surrounded by a layer of large pigment bodies like those 

 which occur scattered in more or less abundance through the skeletal tissue (fig. 5, jj). 

 In other sections again, fibrillar extensions of the central axis pass outwards from it 



1 Comptes rendus, t. xcvii. p. 188. - HI- Cat. Mus. Comp. ZoOL, No. viii. p. 29. 



