326 Revieics — Wachsmuth ^ Springer's Monograph on Crinoids. 



a variety of Cyathocrinus^'), and Tlienarocrinus, in all of which the 

 root was described and figured more than six years ago. The distal 

 end of the stem is likewise known in Gissocrinus, Euspirocrinus, and 

 Bactrocrinus, which also are placed in the Cyathocrinidse on the 

 authority of Wachsmuth and Springer in Eastman's adaptation of 

 Von Zittel's " Palgeontology." 



This section contains numerous interesting observations on the 

 cirri, chiefly of Palaeozoic crinoids. These structures were no doubt 

 less specialized in the older crinoids, especiallj' in Camerata ; but 

 this is no adequate reason for the suggestion that they should 

 "receive a different appellation." Cirri seem to have originated as 

 branchings of the distal end of the stem, radical cirri ; these branches 

 subsequently appeared at higher levels, and became more definite in 

 arrangement ; the cirri in older genera were often large and 

 branched ; they became eventually small in comparison with the 

 stem, unbranched, attached by more definite facets, and with greater 

 activity of movement. But all these changes can be traced ; there 

 is a regular evolution, comparable to the evolution of pinnules ; and 

 as to the homology of the diverse forms, there can be no question. 



Our authors hint that the cirri of Palaeozoic crinoids may have 

 opened out at their ends. " The finest hair-like branches which 

 have come under our observation are perforated at their extremities." 

 They seem to think that the canal of the cirrus may have admitted 

 water to the axial canal of the stem ; they point also to the pores 

 occasionally found in the distal region of the stem as serving the 

 same function ; but they do not seem to have discovered the intimate 

 connection of these pores with the cirri. A branch of the stem 

 naturally contained branches of the axial blood-vessels and nerves ; 

 these became the axial cords of the cirri. After atrophy of the 

 cirri, there still remained the extensions of these soft parts through 

 the wall of the stem, each such extension representing the former 

 attachment of a cirrus. The cavities left by these in the dead 

 stereom are the so-called ' pores ' ; their evolution may be traced in 

 good specimens of the root of Crotalocrinus (Figs. I-IV), but they 

 are not confined to that genus. The greater size of the stem- 

 lumen in so many Palgeozoic genera is explicable on the theory 

 of the evolution of the stem as a plated evagination of perisome 

 such as is seen in some Cystidea ; there is no need to suppose 

 for it any particular function. Its gradual diminution in 

 phylogeny is precisely paralleled by the evolution of the 

 cephalopod siphuncle, which likewise began as a visceral cone. 

 The idea that streams of sea-water passed in through the cirri, or 

 pores, or grooved channels on the under surface of the root, and 

 bathed the folded inner walls of the axial canal as though these 

 were gills, does not seem consistent with the general scheme of 

 crinoid morphology and physiology. It is about as happy as Miller 

 and Gurley's theory that " the mucous or fluid substance, that con- 

 tained the material for the base, passed through the columnar canal 

 into the poi'es of the base and was deposited in a softer state than it 

 afterward assumed." We may, however, suppose that these passages 



