HIE. P. H. CARPENTEE OX THE GENUS ACTINOMETEA. 35 



calcareous segments are regarded by him (pp. 80, 86) as " unverkalkt gebliebene Tlieile 

 dcr biudegewebigeu Grundlage der Kalkgliedcr, deren Aufgabe es ist, aus dem Blutge- 

 f asssystem, genauer aus den fiinf Kammern die kernniihrende Pliissigkeit aufzunebmen 

 und den Arm- und Pinnulagliedern zuzufiihren." 



Without going into the question as to how far the organic basis of the calcareous 

 skeleton can be regarded as of a connective-tissue nature, I would only remark that it 

 is difficult to see why the axial cords, which Ludwig supposes to consist of uncalcified 

 connective-tissue fibres, should give off branches the terminations of which are entirely 

 outside the skeleton, as is the case with those which reach the crescentic leaves at the 

 sides of the tentacular groove, and which therefore cannot take any part in the nutrition 

 of the tissue forming the organic basis of the skeleton. 



(§ 24) This is not the place for a full discussion of Ludwig's views on the nervous 

 system of Comatula ; but one point must be briefly referred to. I have already ^ stated 

 that in some arms, and in most of the jsinnules, of many Actiiwmetrce, the subepithelial 

 band or nerve of Ludwig is entirely absent, and also that "if the axial cords are not 

 nerves, and if the subepithelial bands are to be regarded as the only nervous structures 

 in the whole Crinoid organization, the difficulty presents itself that the oral pinnules of 

 the European Crinoids, and more than half the arms, with the majority of the pinnules 

 of some forms of Actinometra, are entirely devoid of a nervous supply. 



" The oral pinnules of Antedon have been shown by Dr. Carpenter " to be extremely 

 susceptible of irritation ; when they are touched in the living animal, the whole circlet 

 of arms is suddenly and simultaneously coiled up over the disk, "while irritation of one of 

 the ordinary pinnules is simply followed by flexion of the arm which bears it. 



" The structure of these oral pinnules, which are borne in Antedon rosacea by the 

 second brachials, differs very considerably from that of the pinnules borne by the other 

 brachial segments ; for not only are they sterile, but they have neither tentacular appa- 

 ratus nor ambulacral groove, their ventral sm'face being slightly convex instead of being 

 concave as in the ordinary arms and pinnules. This has been mentioned by Teuscher ^ ; 

 but he has omitted to state that the ordinary ciliated epithelium of the ambulacral 

 groove, with its subjacent nervous layer and nerve-vessel, are also absent." Ludwig 

 entirely ignores this argument, although he confirms the above statement concerning the 

 oral pinnules of Antedon ; in the text he is obliged to confess that " Eraglich est mir 

 geblieben ob die oralen Pinnulse einen Zweig des radiaren Nerven besitzen oder nicht " 

 (p. 75) ; while his figure of a section of an oral pinnule (pi. xvii. fig. 55) entirely con- 

 firms the statement quoted above, to which, however, he makes no reference. 



This condition, which is limited in Ant. rosacea to the oral pinnules, sometimes exists 

 in whole arms and in all the pinnules borne by them in many species of Actinometra. 

 Even in the arms which come off from the anterior or oral side of the disk the ambulacral 

 groove does not give off regular branches to the pinnules borne by the third and succes- 

 sive brachial segments ; but a variable number of these first pinnules (sometimes only 



' " Remarks on the Anatomy of the Arms of the Crinoids, part ii.," Journ. of Anat. and Physiol, vol. si. October, 

 1876, p. 89. 



= Proc. Roy. Soc. no. 166, p. 226. = Jenaiecho Zcitsclirift, x. p. 249. 



5* 



