12 BULLETIN 82, UNITED STATES NATIONAL MUSEUM. 



account of the anatomy and embryology of the crinoids, but it is hoped that these 

 points are treated in sufficient detail so that their systematic significance may be 

 appreciated. 



The account of the embryology and of the anatomy of the various forms is 

 taken from the latest and most authoritative works, and will be found to be sufficient 

 for the systematic side of the subject; but it must be emphasized that the extracts 

 given are not intended to be, and are not, sufficient to serve as a basis for anatomical 

 or embryological work, and for such work the original papers, which contain much 

 more than the extracts included here, must be used, as especial care has been taken 

 in order that the information herein given shall not detract in any way from the 

 demand for the original papers by providing an easily accessible transcript of the 

 subject matter or of the figures. 



Methods of microscopical technique are obviously out of place in a systematic 

 work devoted to animals of comparatively large size, and, therefore, are in all cases 

 omitted; they are, however, given in great detail by the authors cited. 



Accounts of obscure anatomical or histologies! points, or discussions with no 

 systematic bearing, are omitted; this includes the discussion of doubtful structures; 

 information in regard to these may be found in abundance in the original papers. 

 The information here given is, it may be again stated, included for systematic work, 

 and from a systematic point of view, only. 



A large amount of exceedingly interesting work has been done on the larval 

 and anatomical homologies of the various echinoderm groups, resulting in a con- 

 siderable diversity of opinion in regard to their interrelationships, and in much 

 speculation as to their common origin and to the original echmodernial prototype. 

 While it is difficult to avoid discussing these matters afresh, it has seemed best to 

 omit reference to them in a work devoted solely to the crinoids, and to only a lim- 

 ited group of the species of that class. The only question that can be of any impor- 

 tance is that of the relationship between the crinoids and the most closely allied 

 classes, and tliis will be considered at some length. 



VARIANTS AND ABEERANTS. 



It has long been recognized that a careful study of variants and aberrants often 

 furnishes most instructive data upon which to base a consideration of the origin and 

 phylogenetic significance of the different organs and members, and of an animal as a 

 whole. In no group is the study of these variants more important than in the echino- 

 derms, and in few groups do they occur with such frequency and along such well- 

 marked lines of progression and retrogression as in the crinoids. 



PHILOSOPHICAL CONCLUSIONS. 



Many general zoological truths are brought out by a study of the crinoids more 

 forcibly than by a study of any other animals, and many others appear in the group 

 in a somewhat new aspect, which sheds a certain very instructive new light upon 

 them. 



For instance, in certain genera most of the species will occupy definite and 

 closely circumscribed areas or depths, each different from that inhabited by any of the 



