DEVELOPMENT OF AJS^TEDON (COMATULA, LAMK.) EOSACEU^. 699 



make their appearance in the latter part of the Pentacrinoid stage (as will be seen by a 

 comparison of figs. a,b, c,d, e in Plate XXXIX. fig. 1), in preparation for that detach- 

 ment of the " summit " from the stem, which thenceforth changes the condition of the 

 animal from the fixed to the free. Notwithstanding that change, the life of the adult 

 Antedon is habitually passed (I feel justified in asserting) so nearly in the same degree 

 of fixedness as that of its Pentacrinoid larva, that it may almost equally be regarded as 

 representing the life of the typical Ckinoidea. If the creature ever quits its attach- 

 ment, save on account of the unsuitableness of its position, it is probably during the 

 period of sexual activity, at which it seems more frequently errant than at any other 

 stage of its life except the earliest. 



11. In regard to the ordinary condition of the Arms, there is much the same variety 

 as is seen among Actinice with respect to the expansion of their tentacles. Sometimes 

 the arms and their pinnae are stretched out quite straight to their full length, and almost 

 entirely in the same plane, so as to present an appearance of rigidity ; whilst sometimes, 

 still remaining fully extended, they are more or less closed together, so as to give to their 

 whole expanse the shape of a funnel more or less deep, with the central disk at its 

 bottom. More commonly, however, some of the arms curve either obliquely or towards 

 the ventral surface ; and this ventral curvature may be so great that the arm forms a 

 spiral which reminds the observer of the unfolding frond of a Fern. Occasionally all 

 the arms are seen to be thus coiled, so that the diameter of the animal is reduced to 

 not more than one-third of that which it has when the arms are fully extended. In no 

 instance have I ever seen the arms more than slightly curved in the dorsal direction ; a 

 peculiarity which will be readily accounted for when we examine the structure of their 

 skeleton in detail. 



12. Whatever may be the purpose of the habitual expansion of the Arms, I feel quite 

 justified in asserting that it is not (as stated by several Authors whom I have cited in my 

 historical summary) the prehension of food. I have continually watched the results of 

 the contact of small animals (as Annelids, or Entomostracan and other small Crustacea) 

 with the arms ; and have never yet seen the smallest attempt on the part of the animal 

 to seize them as prey. Moreover, the tubular tentacula with which the arms are so 

 abundantly furnished have not in the smallest degree that adhesive power which is 

 possessed by the "feet" of the Echinida and Asteriada; so that they are quite inca- 

 pable of assisting in the act of prehension, which must be accomplished, if at all, either 

 by the coiling-up of a single arm, or by the folding-together of all the arms. Now I 

 have never seen such coiling-up of an arm as could bring an object that might be 

 included in it into the near neighbourhood of the mouth ; nor have I seen the contact 

 of small animals with a single arm produce any movement of other arms towards the 

 spot, such as takes place in the prehensile apparatus of other animals. Moreover, any 

 object that could be grasped either by the coiling of one arm, or by the consentaneous 

 closvure of all the arms together upon it, must be far too large to be received into the 

 mouth, which is of small size, and is not distensible like that of the Asteriada. 



