118 BULLETIN 82, UNITED STATES NATIONAL MUSEUM. 



The young of multibradiiate species with a very large number of arms are so 

 totally clifTerenl from tin- adults, and so like the young of other species closely 

 related but with fewer arms, as to render their determination more or less a matter 

 of guesswork unless the characteristic pinnulation is developed. This appears to 

 occur at a very early stage, but in the Comasteridae the pinnules of all the species 

 in each genus are remarkably similar, and even those of different genera vary but 

 little, so that I have usually been quite unable to determine, from the direct evidence 

 furnished by the examination of specimens, to what species, or even groups of species, 

 anv given 10-armed young belongs. Comanthus pinguis, C. japonica, C. solaster, 

 C. trichoptera and C. panicirra are so distinct that typical examples could not 

 possibly be confused; yet there appear to be no characters by which their 10-armed 

 young may be dilTcrentiated. 



The young of the species of Stephanometra in the 10-armed stage superficially 

 somewhat resemble certain species of Oligometra, being, furthermore, of about the 

 same size, and caution nmst be used in order to avoid confusing them, the per- 

 fectly smooth pinnules of the former being, however, sufficiently diagnostic as a 

 rule. 



The young of the species of Ptilomefra (figs. 90, 91, p. 149, 92, p. 151, and 

 adult, 93, p. 153), mainly through the absence of perisomic, side and covering 

 plates, and the rounded arms and pinnules, are more or less like the young of 

 certain antedonids; but the peculiar arrangement of the syzygics and the some- 

 what unusual stoutness, especially of the pinnules and of the cirri, arc sufficient to 

 prevent confusion. 



The arrangement of the syzygies, it may be remarked, is in certain cases one 

 of the most valuable aids in the identification of the young, though care must be 

 used in its employment as a differential character, as it is liable to very considerable 

 change after adolescent autotomy. 



STRUCTURE AND ANATOMY. 



HISTORY OF THE SUBJECT. 



General history. 



The study of the anatomy and physiology of the recent crinoids may be said 

 to have been begun with Adams, who, after a study of living specimens, in a short 

 note published in 1800 pointetl out the existence of two apertures in the disk of 

 Antedon bifida, though he did not recognize them as the mouth and anus. This 

 observation of Adams did not attract the attention that it merited; in 1811 

 de Fr6minvOIe, in diagnosing liis new genus Antedon (which included only one 

 species, A. gorgonia=A. bifida) mentioned that the mouth was central, and on the 

 lower side of the animal. 



P6r()n in ISIO, apparently basing his conclusions on Comatula Solaris, says 

 "bouche inf6rieur, centrale, isol6e, merabraneuse, tubuleuse, saUlante," from which 

 it is clear that he mistook the anal tu])e for the mouth. T.,amarck cjuoted P6ron's 

 notes on the structure of these animals in his monographic account of the group. 



