700 DE. W. B. C^VEPEXTEE OX THE STEUCTUEE, PHYSIOLOGY, AXD 



13. A special function was assigned by Lamarck to what he terms the " rayons 

 simples inferieures," which, as he correctly states, are nothing else than the basal 

 pinnules of the principal arms, "qui sont allongces et abaissees en dessous." He says 

 that these " rayons simples" serve to bring to the mouth the prey which has been 

 captured by the " grands rayons pinnes." This assertion I cannot but consider to be 

 pui-ely hypothetical. It will be shown in the Second Part of this Memoir that there 

 are such peculiarities of structure and disposition on the part of these basal pinnules — 

 which are much longer than the rest, and habitually arch over the central disk (Plate 

 XXXI. a) — as indicate a speciality of function ; but I feel confident that the function 

 assigned by Lamakck cannot be the true one. For not only have I failed to perceive, 

 after long continued obsen'ation and repeated experiments, any such movements of these 

 pinnte as would indicate a prehensile action, but I have found reason to suspect their 

 function to be that of sensorially protecting the soft parts which occupy the ventral 

 surface of the disk, and of preventing unsuitably large particles from being drawn in by 

 the oral cuiTent. For if the ordinary pinnules of any arm be irritated by the contact of 

 a rod, such irritation merely produces a languid wavy motion of the arm thus acted-on, 

 which may extend itself to others if the irritation be repeated or prolonged. But if 

 the rod be made to irritate the long basal pinnules, all the arms (if the animal be in 

 full vigour) immediately close together, -with an energy and consentaneousness that are 

 seen in no other movement. 



14. It was affirmed by M. Dujaedin (I'lnstitut, No. 119, p. 268) that the arms are 

 used for the acquisition of food in a manner altogether dissimilar to ordmary prehension ; 

 for recognizing the fact that the alimentary particles must be of small size, he sup- 

 posed that any such, falling on the ambulacral {\) furrows of the arms or pinnae, are 

 transmitted downwards along those furrows to the mouth wherein they all terminate, by 

 the mechanical action of the digitate papillae which fringe their borders. This doctrine 

 he appears to have subsequently abandoned ; since in his last account of this type (Hist. 

 Nat. des Echinodermes, p. 194) he affirms that the transmission of alimentary particles 

 along the ambulacral {\) furrows is the result of the action of cilia with which their 

 surface is clothed. Although I have not myself succeeded in distinguishing cilia on the 

 surface which forms the floor of these furrows, yet I have distinctly seen such a rapid 

 passage of mmute particles along their groove, as I could not account for in any other 

 mode, and am therefore disposed to believe in their existence. Such a powerful 

 indraught, moreover, must be produced about the region of the mouth, by the action of 

 the large cilia which (as I shall hereafter describe) fringe various parts of the internal 

 wall of the alimentary canal, as would materially aid in the transmission of mmute 

 particles along those portions of the ambulacral {%) furrows which immediately lead 

 towards it ; and it is, I feel satisfied, by the conjoint agency of these two moving powers 

 that the alimentation of Antedon is ordinarily effected. In the very numerous speci- 

 mens from Arran the contents of whose digestive cavity I have examined, I ha^e never 

 found any other than microscopic organisms ; and the abundance of the horny rays of 



