736 DE. W. B. CAEPENTEE ON THE STEIJCTUEE, PHYSIOLOGY, AXD 



whorl of cirrhi is now developed after the same manner as the first, between the latter 

 (with which it alternates in position) and the base of the calyx (Plate XLII. fig. 3); and 

 a third whorl generally makes its appearance before the detachment of the Pentacrinoid, 

 so that the young Antedon possesses ten cirrhi in different stages of advanced develop- 

 ment, and from one io five still rudimentary. 



71. The total length of the full-grown Pentacrinoid, from the base of the Stem to the 

 extremities of the Arms when these are folded together, may be about '7 inch, that 

 of the stem alone being about "25 inch ; when, on the other hand, the arms are fully 

 expanded radially, the diameter of their circle may be about 'S inch. At this period 

 the body and arms usually possess a decided colour, which is sometimes sulphur-yellow, 

 sometimes light crimson, sometimes an intermixture of both hues ; this is usually more 

 pronounced in the arms than in the body, and is entirely due to the development of pig- 

 mentary matter in the minute pyriform vesicles scattered through the sarcodic layer 

 Avhicli still forms, as in the earliest phase of embryonic life', the general envelope of 

 the body and its appendages. 



72. The precise stage of development at which the body of the animal becomes 

 detached from the stem, varies, like that at which a ripening fruit drops off its stalk, 

 according to circumstances. I have met with specimens still attached to their stems, 

 which were larger and more highly coloured than others which were found free ; and I 

 have repeatedly noticed that when kept in captivity they fall off quite spontaneously at 

 an earlier period than that at which they detach thcmseh^es under ordinary circumstances. 

 But the detachment does not seem to take place normally, until the dorsal cirrhi are 

 sufficiently developed to enable them to take the place of the stem functionally by giving 

 the animal the means of attaching itself to fixed objects. 



73. Ilahits. — Concerning the habits of the Pentacrinoid I have little to add to what 

 has been already noticed by Mr. J. V. Thompson^ "The animal," he says, "possesses 

 the power of bending or inclining the stem freely in every direction ; and what is more 

 remarkable, of twisting it up into a short spiral, and that, with a considerable degree of 

 vivacity, — a kind of movement that has noi, been noticed except in the Vortieellce." He 

 speaks of the arms as " at one time spreading outwards like the petals of a flower, at 

 another, rolled inwards like an expanding bud ; " and continues, — " From their structure 

 and movements it can hardly be doubted that they serve to seize upon and convey to the 

 mouth whatever has been destined for its food, and which probably consists in every 

 minute animal its powers enable it to overcome." Now, whilst I am quite at one with 

 this excellent observer as to the facts which he records, I differ from him in regard to 

 their interpretation ; for I have seen nothing to make me believe that in the Fentacri- 

 noid, any more than in the adult Antedon, are the arms ever employed for prehension ; 

 whilst the existence of large vibratile cilia on the walls of the digestive cavity, as seen by 

 Professor Wtville Thomson in the early Pentacrinoid, and by myself in the more 



' Sec Professor Wr\'iLLE Thomson's Memoir, Philosophical Transactions, 1865, pp. 522, 535. 

 ' Memoir on the Pentacrtmis EurojMus, p. 7. 



