DEVELOPIVIENT OF AJfTEDON (COMATULA, LAMK.) EOSACEUS. 



709 



with him in the following statement (op. cit, p. 7): "These filaments are not all alike; 

 there are two kinds of them. The larger have fourteen joints, and a small thick, blunt, 

 curved claw, which is smaller than the joints, and has a homy lustre : the smaller fila- 

 ments have eigliteen rough joints, and an almost straight claw, which is larger than the 

 joints preceding it." I shall presently show that the first-named form is that of the ftdly 

 developed cirrhus, whilst the latter (save as to the number of joints) is that of the same 

 organ in an earlier stage of its development ; and that occasionally (though rarely) the 

 rudimental fonn is retained with an increase in" the number of joints beyond the average. 

 In each of eleven out of the twelve specimens, in which I have examined the cirrhi with 

 great care, I have found the predominant number of segments, excluding the one which 

 bears the claw, to be 15 ; but in at least one-third of the cirrhi in each of these speci- 

 mens (excluding those which retained their rudimental characters) the number of 

 segments is below that standard, ranging from 14 to 10, and in a few instances to 9. 

 In the single exceptional specimen, the predominant number of segments was 16, and 

 one cirrhus had 17 (besides the claw); and this number I have never found exceeded, 

 though the whole number of cirrhi whose joints I have counted exceeds 300. In twO 

 ciiThi retaining the rudimental form, I have counted 17 segments besides the claw; 

 but I have never found this number exceeded'. 



27. The typical form of the Dorsal Cirrhi is represented in Plate XXXII. fig. 5, a; 

 in which we notice (1) that the cirrhus is curved along a great part of its length in the 

 same direction as its terminal claw, the distinction being thus marked between its 

 convex or oral and its concave or aboral border ; (2) that the basal segments are short, 

 their diameter considerably exceeding their length, and are cylindrical, or nearly so ; 

 (3) that there is a progressive increase both in the length and in the diameter of the 

 segments as far as the 11th joint, this increase being at first so much more rapid in 

 length than in diameter that the 5th, 6th, 7th, and 8th segments are considerably longer 

 than they are broad, approaching the proportion of 3 : 2 ^ Avith some degree of lateral 

 compression ; (4) that beyond the 11th joint the length of the segments again dimi- 

 nishes, their diameter remaining nearly the same ; (5) that the last segment has attached 

 to it by simple suture a strong, sharp claw, and is itself prolonged at the base of this, 

 on its aboral margin, into a short pointed opposing process^. Between the segments is 



Ross-shire, one specimen of whicli possesses 42 dorsal cirrhi of which 7 are rudimental, and another 46 of which 

 8 are rudimental. 



' The number of joints in the cirrhi of Comatula Mediterranea is stated by Professor J. MtJiiER to be 18-20, 

 and by DujARDiif to bo about 20. 



^ I am particular in the statement of these proportions, because they have been employed on insufficient 

 grounds (as I believe) by Professor "Wttille Thomson as a character of specific distinction betweew A. rosaeeus 

 and A. Milleri. 



' This process, as I shall presently show, is almost always wanting in cirrhi which have not attained their full 

 development; and as it is not unfrequently absentia such as show no other characters of immaturity, I 

 cannot agree with Professor "Wtville Thomson {loc. cit.) in regarding the possession of this opposing process as 

 a valid specific character of A. rosaceus. 



