70 ME, P. H. CAEPENTEE ON THE GENUS ACTINOMETEA. 



stem being first shed and their sockets filled up by new deposit, and the space thus 

 formed being gradually widened by the progressive exuviation of the cirrhi that bound 

 it, and the filling up of their sockets." Thus the flattened central portion of the 

 dorsal surface of the plate by which it was originally attached to the joint of the stem 

 next beneath it increases very much in extent, and finally comes to bear a considerable 

 proportion to its diameter (PL IV. fig. 1). In Act. polymorpha (PI. VI. figs. 2, 7, 14, 

 16, 20), as we have seen, it extends over the whole of the dorsal surface of the plate, and 

 to a certain extent also in Act. robusta (PI. V. fig. 15). In Ant. Hschrichtii, however, it 

 does not reach any great extent, for most of the first-formed cirrhi do not appear to be 

 cast off as in Ant. rosacea and Ant. ecltica, or, if they are lost, their sockets are not obli- 

 terated, but they seem to be replaced by others, for I have frequently found young and 

 rudimentary cirrhi among the larger and perfectly developed ones around the central 

 portion of the large hemispherical " Knopf" of this species l . 



(§ IS) In most pedunculate Crinoids, in which the calyx rests upon the uppermost 

 segment of the stem, this segment, instead of being the largest, is the smallest, being 

 the latest formed, while the base of the calyx is formed by the thickened and expanded 

 basals. Hence, as Dr. Carpenter remarks 2 , "it seems clear that the extraordinary 

 development of the highest segment of the stem into the centrodorsal basin, which is 

 characteristic of the mature Antedon, is connected with the multiplication of the pre- 

 hensile cirrhi which extend themselves from its dorsal surface." 



At the base of the quinquelocular organ, and lying on the bottom of the centrodorsal 

 basin, but enclosed, together with the five chambers, in the above-mentioned fibrillar 

 envelope (JV), winch is probably of a nervous nature, there is, both in Antedon and in 

 Actinometra, a succession of verticils of five triangular leaflets 3 . As already shown by 

 Dr. Carpenter, there can be little doubt but that the lower ones of these mark the 

 origins of the earlier cirrhal cords from the crinoidal axis. They increase in size from 

 below upwards, and from the extremities of some of the upper leaflets there issue groups 

 of three diverging cords that proceed to the cirrhi which are developed at a later period 

 around the periphery of the centrodorsal piece. 



Greeff i has found the older cirrhus-cords still in connexion with these leaflets. 

 Apparently unaware of the original existence and subsequent removal of the cirrhi cor- 

 responding to them, he drew a distinction between the vessels which they enclose, and 

 which end close under the dorsal surface of the plate, and the vessels enclosed in the 



1 I cannot altogether confirm Mailer's statement (' Gattung Comatula,' p. 239 (3) ) that the central apical portion of 

 the centrodorsal in Ant. Eschrichtii, where it was formerly united to the stem, may be covered with cirrhi. In all 

 the individuals of this species which I have examined (and they are many) there is always a small apical space 

 quite free from cirrhi ; it may not bo wider than the diameter of a large cirrhus-sockct, but it is always to be found. 

 I imagine that by the expression " Da es Antedon-Arten giebt, bei denen auch der mittlere Theil des C'entrodorsale 

 Cirrhen tragt (Antedon Eschrichtii v.. \\.) " (Crinoideen, p. 69, note), Ludwig does not mean any thing more than 

 that the centrodorsal is covered with cirrhi to a much greater extent than is usual in most Comatulce, where there is 

 generally a central space of considerable extent entirely free from cirrhi. Schliiter lias also expressed his doubts 

 respecting the accuracy of Midler's statement. 



■ Proceedings 11. S., No. 100, 1870, p. 218. 3 These are seen in section in PI. VIII. figs. 3, 7. 



4 Marburg Sifzungsberichte, No. 5, 1S76, p. 91. 



