32 ME. p. H. CAEPENTER OX THE GENUS ACTIXOMETEA. 



The position of the point at wliich the two folds of perisome bounding the sides of the 

 original anil)ulaeral groove meet and unite, varies extremely. The fusion may, tlioug'h 

 rarely, take place on the disk ; sometimes it is at the base 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 ambulacral groove is entirely 

 obliterated. 



(§ 23) The bearings of this fact iipon the difTerent views advanced by Greeff ^ and 

 Ludwig - respecting the homologies of the ambulacral grooves of the Crinoids will be 

 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 be 

 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 18G5 it was stated by Dr. Carpenter * that the cord which traverses the 

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

 by Professor Miiller 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 Mviller 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 i 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 Miiller 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 bishcr immer als Gefass aufgefasste Strang im innern des Kalkskelettes 

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

 cin Gano-lion anzuschcn." 



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

 overlooked for many years, so that even as late as 1874 Miiller's erroneous statements 

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

 of Gegenbaur^ and in many smaller Avorks. At the commencement of 187G, however, 

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

 taneously by GreelT and by Dr. Carpenter. The former '^ 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 



" Ueber den Bau der Echinodcrmcn. III. Mittlieilung," Sitzungsb. der Gesell. z. Boforder. d. gesamm. Natunviss. 

 zu Marburg, ISTlJ, No. 1 1 , p. 1 55. 



- " Beitr. z. Anat. der Criiioideen," Nachrichten von dor Konigl. Ocsclls. der Wisscns. u. dor G. A. TJniversitiit 

 zu Gcittingen, 187G, No. 5, pp. 107, 108. 



" "Researches on tlio Structure, Physiology, and Development of Antcdon rosaceus. Parti.," Philos. Trans, 

 vol. clvi. p. 705. 



•• " Kurzc anatom. Bcmerk. iiber Coma<u7rt," Arbeit, aus d. zool.-zootom. Inst.zuWUrzburg, Band i. (1874), p. 262. 



' Gnindriss der vergleich. Anat. p. 22i!. 



' " Ueber den Bau dor Crinoidcen," Jlarburg. Sitzungsb. 1«7C, No. 1, Jan. 13, p. 21. 



