108 THE VOYAGE OF H.M.S. CHALLENGER. 



This divides into two or more which pass upwards, like the chambers themselves into the 

 glandular organ above (PL XXIV. fig. 6 ; PI. LVIII. fig. 3—V; PI. LXIL). But a sieve- 

 like axis, such as occurs in Antedon, is absent in the stalked Crinoids, which have no 

 cirri just beneath the calyx that require to be supj^lied with blood. 



E. The Genital Glands. 



Since the discovery, made independently by Dr. Carpenter and Prof. Semper,^ 

 that the so-called nerve of Miiller, which is situated between the skeleton and the water- 

 vessel of the Crinoid arm, is really a part of the generative system, our knowledge of its 

 minute anatomy has been largely increased by Ludwig. 



He discovered that the actual genital tube, the epithelial cells of which develo]) into 

 ova (PL Vb. fig. 1 ; PL Vc. fig. 1 ; PL Villa, figs. 4, 5 ; PL LX. fig. &—gc.), is suspended 

 by fusiform or branched cells within a blood-vessel ; and he believed this vessel to arise 

 from the vascular plexus underlying the subtentacular canals of the disk. 



Dr. Carpenter had previously come to the conclusion, as the result of his dissections, 

 that the genital cord or so-called rachis of the arm is a radial extension of this plexus. 

 He further believed the latter to be in connection with the ventral end of the plexiform 

 gland, having seen the division of this organ in the Pentacrinoid into five branches, one 

 of which passes to each ray, an observation which may be easily confirmed by examina- 

 tion of optical sections of a Pentacrinoid, soon after the appearance of its first whorl of 

 cirri. According to Perrier the body-cavity of a mature Pentacrinoid or recently 

 liberated Comatula contains no structures wliieh could be considered as blood-vessels ; 

 although he finds within the meshwork of connective tissue that occupies the body-cavity 

 "un petit nombre de cordons ceUulaires pleius qui se rendent manifestement aux bras"^ 

 I have little doubt that these are a further development of the branches from the axial 

 organ of which one pas-ses to each ray, as described by Dr. Carpenter ; and that they 

 eventually give rise to the subambulacral plexus of genital vessels (PL LVII. fig. 3; 

 PL LX. figs. 1, 2—gv). 



The genital tube of the arm is regarded by Ludwig as a sterile portion of a complex 

 genital orgau,^ the epithelial lining of which only develops into ova or spermatozoa in 

 particular places, usually within the pinnules. The ceUs lining it are relatively large, and 

 project into its interior, thereby reducing its cavity very considerably. 



Dr. Carpenter, who was unacquainted with the blood-vessel ensheathing the true 

 genital cord, spoke of the latter as having a tubular wall and granular contents ;* and he 

 stated that in the plexus beneath the subtentacular canals of the disk of Antedon rosacea 



' Kurze anatomische Bemerkungen iiber Comatula, Arb. zool.-zootom. Inst. Wiirzhurg, Bd. i. p. 260 ; translated, 

 with -MX Addendum by Dr. Carpenter in the Ann. and Mag. Nat. Hist., ser. 4, vol. xvi., 1875, pp. 202-209. 

 ^ Comptes rendiis, t. xcviii. p. 445. ' Crinoideen, loc. cit., p. 293. 



* Proc. Hoy. Soc. Land., 1876, pp. 220, 221. 



