072 DR. W. B. CAEPENTEll ON THE STRUCTUEE, PHYSIOLOGY, AND 



The peculiar interest oi Antedon as a "typical form" arises from its being the only 

 representative now left in British seas of that wonderful Order Crixoidea, Avhich, under 

 various modifications, has maintained its place in our Fauna from the Silurian epoch to 

 the latest Tertiary period. It is true that in some important particulars, Antedon is a 

 less characteristic representative of the Crinoidea than is the existing Fentacrinus 

 of the West Indian seas ; and a complete Monograph of the structure and life-history 

 of that organism would be one of the most valuable contributions which Palaeo-zoolo- 

 gical science could receive. But for such a Monograph there is unfortunately no rea- 

 sonable ground of hope. Tlie rarity with which specimens of tliis Fentacrinus have 

 occurred, and the imperfection of the state in which they have been preseiTed, have 

 hitherto prevented any save a very unsatisfactory account of its structure from being 

 given ; although the best of tliese specimens fell under the examination of an Anatomist 

 and Physiologist no less able than Professor Joiiann Mxjllkk. And even supposing that 

 a fortunate chance should throw a perfect and well-preserved specimen in the way of 

 some equally accomplished Naturalist, he could do no more than give a minute descrip- 

 tion of its organization ; — a knowledge of its life-history being likely to remain unattain- 

 able, on account both of the rarity of the species and of the great depths at which alone 

 it is found. 



Moreover, although in its adult state Antedon seems to depart widely from the typical 

 Crinoids, in having neither root nor stem, and in possessing a power of free locomotion 

 of which they are altogether destitute, yet tins departure involves what is really (in a 

 physiological point of view) the least essential part of the Crinoidal fabric; — a part, 

 moreover, which exists in that earlier stage of this animal's life, wherein it is in this as 

 in all other particulars a true Crinoid ; and which is afterwards replaced, so far as its 

 function is concerned, by a prehensile apparatus that is subservient to the very same 

 purpose. For, as I shall show hereafter, the mature Antedon habitually clings by its 

 dorsal cirrlii to a fixed attachment, so as to resemble its Pentacrinoid larva in its ordinary 

 habit ; iising its power of free locomotion only when persistence in its position would 

 be no longer conformable to its requirements. 



It has been, therefore, because every addition to our knowledge of Antedon contributes 

 to the elucidation of the structure, physiology, and life-history of the Ceixoidea gene- 

 rally, that I have thought it Avorth while for some years past to devote a considerable 

 portion of such brief periods of leisure as I have been able to command, to the careful 

 study of the species (A, rosaceus) which presents itself abundantly on various parts of 

 our northern, western, and southern shores. When I commenced this study, I enter- 

 tained the hope of being able to trace out the whole history of its development, from the 

 very commencement of its existence as a free-swimming larva. But I soon found that 

 the earlier stages of this process take place during a part of the year in which my official 

 duties do not allow of my visiting the coast ; and learning that Professor Wttille 

 Thomson was able and willing to undertake this part of the inquiry, I gladly arranged 

 with him that he should work out the developmental history of Antedon as far as the 



