ANTEDON 903 



anchor the animal when it drops from the stem ; this supports the 

 basals, on which rest the first radials (r l ) ; whilst the anal plate is 

 now lifted nearly to the level of the second radials (r 2 ) by the 

 development of the anal funnel or vent to which it is attached. The 

 oral plates are not at first apparent, as they no longer occupy their 

 first position ; but on being carefully looked for they are found still 

 to form a circlet around the mouth (3, o, o), not having undergone 

 any increase in size, whilst the visceral disc and the calyx in which 

 it is lodged have greatly extended. These oral plates finally dis- 

 appear by absorption ; while the basals are at first concealed by the 

 great enlargement of the centro-dorsal (which finally extends so far 

 as to conceal the first radials also) ; and at last undergo metamor- 

 phosis into a beautiful ' rosette, >which lies between the cavity of the 

 centro-dorsal and that of the calyx. In common with other members 

 of its class, the Antedon is represented in its earliest phase of develop- 

 ment by a free-swimming ' larval zooid ' or pseudembryo^ which was 

 first observed by Busch, and has been since carefully studied by 

 Professors Wyville Thomson ] and Goette. 2 This zooid has an 

 elongated egg-like form, and is furnished with transverse bands of 

 cilia and with a mouth and anus of its own. After a time, how- 

 ever, rudiments of the calcareous plates forming the stem and calyx 

 begin to show themselves in its interior ; a disc is then formed at the 

 posterior extremity by which it attaches itself to a seaweed (very 

 commonly Laminaria), zoophyte, or polyzoary ; the calyx containing 

 the true stomach, with its central mouth surrounded by tentacles, is 

 gradually evolved ; and the sarcodic substance of the pseudembryo, 

 by which this calyx and the rudimentary stem were originally in- 

 vested, gradually shrinks, until the young pentacrinoid presents 

 itself in its characteristic form and proportions. 3 



1 ' On the Development of Antedon rosaceus' in Phil. Trans, for 1865, p. 513. 



2 Archiv f. mikrosk. Anat. Bd. xii. p. 583. 



5 The general results of the Author's own later studies of this most interesting 

 type (the key to the life-history of the entire geological succession of Crinoidea) are 

 embodied in a notice communicated to the Proceedings of the Royal Society for 

 1876, p. 211, and in a subsequent note, p. 451. Of the further contributions recently 

 made to our knowledge of it the memoir of Dr. H. Ludwig ' Zur Anatomic der 

 Crinoideen ' (Leipzig, 1877), forming part of his Morphologische Studien an Echino- 

 dermen, is the most important. Those who wish to carry further their study of the 

 Crinoidea should consult the two monographs by Dr. P. Herbert Carpenter in the 

 ' Challenger ' Reports. 



COLLEGE OF DENTISTRY 

 UNIVERSITY OF CALIFORNIA 



