31 



They may Lave been used as conduits for the waste material 

 that entered through the ambulacral furrows, or for the discharge 

 of surphis water, but whatever their purpose they must have been 

 used in the performance of some important physiological function. 

 There would seem to be no doubt of that fact. This conclusion 

 leads us to ask why, if they were so important to the species pos- 

 sessing them, did the greater number of species in the genus ex- 

 ist without them? The question is unanswered and at present un- 

 answerable, because the physiological functions performed, at the 

 seat of life, which is supposed to have been near the central part 

 and on a level with the top of the calyx, in this genus of palaeo- 

 zoic crinoids, are not known. The orifices are elongated externally 

 and in their passage througii the vault, because they are directed 

 horizontally through the convex vault, and the elongation, there- 

 fore, depends upon the convexity of the vault in the different spe- 

 cies. 



CRINOID BASES. 



Plate III, Fig. 13, siq)erior side of an eroded base; Fig. 14, in- 

 ferior side of same. 



Crinoid bases are as full of pores as sponges and, when silici- 

 fied, they may be cleaned with acid and made to expose the pores 

 as shown in the illustrations. Weathered specimens, when not 

 silicified, expose the pores, and a broken fragment will expose 

 them also. Unaltered and finely preserved specimens do not expose 

 the pores externally. The column is inserted in an obconoidal 

 cavity in the base and the pores radiate from this cavity in all di- 

 rections to the farthest extremities of the base. They are rarely 

 larger than an ordinary sewing needle, and generally less in size, 

 but so numerous that the interspaces have a diameter but little 

 more than the diameter of the pores. The radiating pores are 

 more or less sinuous and accommodated to the irregularities of 

 the base. 



These pores, as we suppose, were connected with the columnar 

 canal and through them the material passed that formed the base. 

 The histogenesis of the base may be compared with the formation 

 and development of the bones of an animal. 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 



