32 ME. P. H. CARPENTER ON THE GENUS ACTINOMETEA. 



The position of the point at which the two folds of perisonie hounding the sides of the 

 original ainbulacral groove meet and unite, varies extremely. The fusion may, though 

 rarely, take place on the disk ; sometimes it is at the hase of the arms, and sometimes 

 not till near their middle or terminal portions. In any case, however, the fusion, when- 

 ever it occurs, is so complete that all trace of the original ainbulacral groove is entirely 

 obliterated. 



(§ 23) The bearings of this fact upon the different views advanced by Greeff l and 

 Ludwig 2 respecting the homologies of the ainbulacral grooves of the Crinoids will he 

 best discussed at a later period, when the changes undergone by the various structures 

 underlying the grooves are described and illustrated. One point, however, must he 

 noticed here on account of its importance with respect to the two views now entertained 

 regarding the nervous system of Comatula. 



As long ago as 1865 it was stated by Dr. Carpenter 3 that the cord which traverses the 

 length of the arms between the subtentacular and cceliac canals, " and which was regarded 

 by Professor Miillcr as a nerve, really belongs to the reproductive apparatus. But it 

 will also be shown that a regular system of branching fibres proceeding from the solid 

 cord (described by Professor Miillcr as a vessel) that traverses the axial canal of each 

 calcareous segment of the rays and arms, is traceable on the extremities of the mus- 

 cular bundles ; and reasons will be given for regarding these fibres as probably having 

 the function of nerves, though not exhibiting their characteristic structure." During 

 his residence in the Philippine Islands, Professor Semper had also discovered that the 

 arm-nerve of Miillcr is really a part of the generative system ; and in a short paper * 

 published some time after his return he announced this fact, and suggested at the same 

 time, " dass der lusher immer als Gefass aufgefasste Strang im innern des Kalkskelettes 

 ein Nervenstrang sei, und dann ware wohl das im Kelch liegende sogenannte Herz als 

 ein Ganglion anzusehen." 



These observations of Dr. Carpenter's and Professor Semper's were unfortunately 

 overlooked for many years, so that even as late as 1871 Midler's erroneous statements 

 with regard to the nervous system of Comatula were repeated in the valuable text-book 

 of Gegenbaur 5 and in many smaller works. At the commencement of 1876, however, 

 two very different views respecting the nervous system were put forward nearly simul- 

 taneously by Greeff and by Dr. Carpenter. The former 6 described the whole floor of the 

 ambulacral grooves on the arms and disk of Ant. rosacea as constituting a radial 

 nervous system, starting from an oral nervous ring in the peristome, and corresponding 



" Peber den Bail der Echinodermen. III. Mittheilung," Sitzungsb. der Gesell. z. Beforder. d. gesamm. Naturwiss. 

 zu Marburg, 1S72, No. 11, p. 155. 



- - Beitr. z. Anat. der Crinoideen," Nachrichten von der Konigl. Gesells. der "Wissens. u. der G. A. Universitat 

 zu Giifctingen, 1876, No. 5, pp. 107, 10S. 



3 " Researches on the Structure, Physiology, and Development of Antedon rosaceus. Tart I.," Philos. Trans, 

 vol. clvi. p. 705. 



J " Kurze anatom. Bemerk. iiber Comatula," Arbeit, aus d. zool.-zootom. Inst. zuWurzburg, Band i. (lS74),p. 262. 



5 Grundriss der vergleich. Anat. p. 222. 



6 '• Peber den Bau der Crinoideen," Marburg. Sitzungsb. 1»70, No. 1, Jan. ^^6, p. 21. 



