THE CRINOIDEA 



'33 



vascular and nervous prolongations of the chambered organ and 

 axial organ to columnals and cirrals, may in some earlier forms 

 have served other purposes. The lumen is sometimes extra- 

 ordinarily wide (40 mm. in the root of Barycrinus, Fig. XVI. 3). 

 Pores sometimes appear to exist between or through the colum- 

 nals (e.g. Barycrinus, Crotalocrinus, Fig. L., Traumatocrinus). The 

 distal ends of the cirri sometimes appear to have been open, so 

 that the large axial canal communicated with the sea -water 

 (e.g. Barycrinus, Eucalyptocrinus, Cystocrinus, Fig. L. 2). The flat 

 under surface of encrusting roots is often ridged, as though 

 grooves put the axial canal in connection with the exterior (e.g. 

 Lichenocrinus, in which the upper surface is formed of poly- 

 gonal plates, supported beneath by numerous radiating lamellae). 

 These bases of attachment are, say Miller & Gurley, " as full of 



FIG. L. 



The development of "pores" from 

 cirri. 1, Crotulocrinus, portion of root, 

 with branching cirri below, and attach- 

 ments of cirri in upper part. These 

 latter show the axial canal that passes 

 from the main axial canal of the stem, 

 through the thickness of the colnmnals, 

 to each cirrus, and continues to the end 

 of the cirrus. Nat. size. 2, Cystncrinus 

 tennesseensis, part of stem, showing 

 stumpy aborted cirri, wit'.i axial canals 

 opening at their ends. Nat. size. 3, 

 Crotalocrinns, part of stem, showing 

 crenulate sutures between columnals, 

 and on the columnals the atrophied 

 attachments of cirri ; compare with the 

 extreme upper part of tig. 1. x 5 diam. 

 4, Crotalncrimis, part of stem, showing 

 total disappearance of cirrus-attachment, 

 and only the axial canals remaining as 

 "pores" piercing the columnals. x 5 

 diam. (From Bather, 1898.) 



pores as sponges." On the theory here adopted as to the origin 

 of the stem, a greater exten. n of the viscera into it in early 

 forms is probable ; the chambered organ itself may have been 

 placed some way down it (compare evolution of siphuncle from 

 visceral cone in Cephalopoda). Assuming that the soft structures 

 contained in the stem-lumen needed aeration, Wachsmuth & 

 Springer have supposed that streams of sea - water entered 

 by these pores. This suggestion seems no more happy than 

 Miller & Gurley's idea that "the mucous or fluid substance, 

 that contained the material for the base, passed through the 

 columnar canal into the pores of the base and was deposited in 

 a softer state than it afterward assumed.'' We may, however, 

 suppose that these passages served the double purpose of trans- 

 mitting nutrient fluid to the mesoderm cells depositing the outer 

 layers of stereom as the stem and root grew wider by concentric 

 accretion, and of aerating the same fluid by bringing it near the 

 oxygenated sea-water. 



-C* 



