. Carnegie Institution of Washington publication. GENERAL PART. 79 as Carpenter says, that one of the rami grows faster than the other, but it is the pinnule which grows faster than the arm-joint and soon reaches beyond it, but it never "takes a line continuous with that of the axis of the arm," as Carpenter thought it did. The Crinoid arm is thus no sympodium, but in reality what it has the appearance of being—a single arm with small alternating side-branches, the pinnules. The place of formation of new joints in the growing pinnules was not made out with certainty by Carpenter; he
. Carnegie Institution of Washington publication. GENERAL PART. 79 as Carpenter says, that one of the rami grows faster than the other, but it is the pinnule which grows faster than the arm-joint and soon reaches beyond it, but it never "takes a line continuous with that of the axis of the arm," as Carpenter thought it did. The Crinoid arm is thus no sympodium, but in reality what it has the appearance of being—a single arm with small alternating side-branches, the pinnules. The place of formation of new joints in the growing pinnules was not made out with certainty by Carpenter; he came to the conclusion that "it may be safely assumed that they are not developed at the terminations of the pinnules, since their peculiar terminal hook is formed when as yet the segments are few in ; The new joints must then be intercalated "either between the basal and the second segment, or between the penultimate segment and the terminal claw-bearing segment. Since no such traces of incompleteness present them- selves in the segments which follow the basal as would justify the former supposi- tion, we seem compelled to adopt the latter; and it is not a little curious that the increase in the number of segments in the Stem, the Dorsal Cjrrhi, the Arms, and the Pinnules should thus take place in different modes—the new segments mak- ing their appearance in the Stem immedi- ately beneath its highest segment, in each Dorsal Cirrhus at its base, in each Arm at its termination, and in each Pinnule at the base of its terminal ; (W. B. Carpenter, op. cit., pages 747-748.) That Carpenter is mistaken in this point is easily ascertained by a closer examination of the newly formed pinnules at the point of the arm. The new joints are formed at the tip of the pinnule, and the terminal hook is the last to form. All the joints are formed in the course of a very short time, while the pinnule is still very short; already in the third pinnule from the p
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