ro8 



DE. "W. B. CAEPENTEE OX TILE STEUCTTJEE, PHYSIOLOGY, JlKD 



out or nearly so, considerably beyond the margin of the disk. These appendages, for 

 which it seems to me that the designation given by Lamarck and adopted by Uujaedin is 

 the most appropriate, were termed by J. S. Miller " auxiliary side arms," by Blahn^tille 

 " rayons auxiliaires," by Professor J. Muller '• ranken," and by Professor Edward Forbes 

 "filaments, jointed appendages, or simple arms." Any name which indicates a resem- 

 blance between these cirrhi and the Rays or Arms belonging to the calyx, is most inap- 

 propriate ; since the two sets of organs have no other point of resemblance than that 

 which consists in the articulated structure of their skeleton, whilst they differ in toto 

 as regards both their homological relations and their functional uses. The designations 

 respectively applied to them by J. S. Miller and by Blaiktille were so far correct, as 

 indicating their homology with those appendages of the stem in Pentacrimis which 

 these authors distinguished by the same terms ; and it is expressly stated by the former 

 that " these arms, the formation of their joints, and their hook-like termmation, resemble 

 in every particular those of Pentacrinus Caput-Medusce, only that they are much shorter, 

 and formed of a less number of jomts." That the " dorsal cirrhi " of Antedon have no 

 other function than that of mechanically fixing the animal, appears alike from the 

 extreme simplicity of their stnicture (which presents not the smallest trace of the com- 

 plex apparatus that is extended throughout the vrhole of the true brachial appendages), 

 and from observation of the animal in its lining condition, as I have akeady shown in 

 the description of its habits (§§ 9, 10). 



2G. The member of the Dorsal Cirrhi in Antedon rosaceus is by no means constant, nor 

 is their size uniform. It is by no means uncommon to find, even on the largest speci- 

 mens, one, two, three, and sometimes more of these organs in a very rudimental condi- 

 tion ; such being usually interposed between the larger ones at the extreme circum- 

 ference of the Centro-dorsal plate. In order to ascertain the range of variation in this 

 character (to A^hicli some systematists attach considerable importance in the discrimina- 

 tion of species), I have carefully removed and laid upon separate tablets the entire clus- 

 ters of cirrhi possessed by twelve Arran specimens, Avhich, although differing in size, 

 all presented every appearance of maturity ; and I find the respective numbers of these 



organs to be as follows : — 



21, of which 3 were rudimental. 



VII. 27, of which 3 were rudimental. 

 VIII. 29, „ 2 



29, 

 30, 



IX. 

 X. 



XI. 32, 

 XII. 32, 





 2 

 4 

 1 



Thus it appears that Professor Edward Forbes was not far wrong in stating the number 



of these organs to be from twenty to thirty^. I cannot, however, by any means agree 



' History of Britisli Starfishes, p. 7. The numher of cirrhi iu Comattda Mediterranea is stated by Laiiaeck 

 at 30, by Professor Joh. Muller at 30-40, and by DrjAEDix at 20-26. — I have lately had the opportunity, 

 through the kindness of Mr. J. Gwr?? Jeffekts, of examining a variety of Antedoii rosaceus from the coast of 



