130 THE CRINOIDEA 



a disc. We may, with Wachsmuth & Springer, regard the exten- 

 sions as caused by the perforation of the plates for water-canals ; 

 or we may regard them as simple processes for the purpose of 

 adding strength, without forgoing lightness, by a system of girders. 

 The supposition just quoted, as to the existence in Camerata 

 of a complicated water -vascular system, is supported by the 



connection of the internal passages 

 with small pores near the arm-bases 

 (Fig. XLV.). Such have been ob- 

 served by Wachsmuth & Springer 

 in Actinocrinidae, Batocrinidae, 

 Rhodocrinidae, and Melocrinidae ; 

 l 2 they are placed in the cup-wall at 



*" 10 ' XLV the level of the tegmen, between the 



Pores in Camerata. 1, DafotorflMU t ^-t - i i 



Lyoni, an interrudins, showing siit-iike armsand their rami, and their canals 



are separated from the subtegminal 

 arm-grooves by a thin partition. 



(from Brit. Mns. specimen 755!2). x t). In JlatOCnniLS, StrotOCnilUS, StegaUO- 

 .ecal cavity. ^^ Eudadocrinu ^ and others in 



which the arms branch off alternately, there is a pore to each ramus 

 that springs directly from the dorsal cup. Dolatocrinus may have 

 four to six in each interradius, and two to four between each IIBr 

 series. Other genera have only ten pores. In Gilbertsocrinus these 

 are at the end of long tubular extensions of the iriterradial areas 

 (Fig. CXXVIL). The facts are so plain, that the introduction of 

 water into the thecal cavity for aeration of the viscera seems prob- 

 able ; but the connection of these passages with the hydrocoel or 

 with branches thereof is a different question. The pores may pos- 

 sibly have replaced the hydropore or the madreporite of certain 

 Inadunata. In many recent crinoids pores pierce not only the 0. 

 but the iAmb, often in great numbers, being least numerous in 

 the posterior IR. Antedon bifida (Fig. XLVI.) is said to have 1500. 

 They may also occur on the edge of the theca between the arms. 

 In Actinometra they are chiefly developed near the ventral grooves, 

 and even on the pinnules. These pores communicate with the 

 coelom or its extensions (Fig. XLVIL), and so indirectly with the 

 water-ring. Where there are few pores (e.g. Rhizocrinus, Fig. X.), 

 a process (stone-canal) stretches out towards each from the ring ; 

 but, when numerous, there is no correspondence between stone- 

 canals and pores. 



The statement has repeatedly been made (by Trautschold, 

 Lov^n, Wachsmuth & Springer) that pores occur on the suture- 

 lines between the plates composing the anal tube of many 

 Inadunata. In the cases to which the last-named authors now 

 restrict the statement, the tube-plates have strong axial folds, being 

 no doubt connected along these by thicker ligament, innervated from 



