BASAL PLATES IN CRINOIDEA CAMERATA 



5°3 



cells, but take the calcareous salts into solution and transmit them 

 to the deposition cells. 1 When reduction by proximal or distal, or 

 proximal and distal, absorption is symmetrical throughout a cycle 

 of plates, the relation of parts is not disturbed, unless the reduction 



N 



V 







'%>T~ 





Fig. 4. 4 — Stereom absorption; absorptive cells operating upon the posterior end 

 of a calcareous rod in a mature pluteus: 1, one portion of rod separated, the second 

 partially cut; 2-4, advancing stages up to the nearly completed absorption of portion 

 one, the separation of portion two (after Theel) . 



of the cycle is complete, thus bringing previously separated cycles 

 into apposition with each other. 



c) Anchylosis. — Anchylosis is the uniting of apposed plates by 

 an unbroken deposit of stereom in the sutures, and is, as far as we 

 know, an ontogenetically repetitive process, taking place only 



J Ref. 34, pp. 349-351- 



