42 o • Eeport oi THE State Geologist. 



come at last to touch and to close, so that no trace of its existence 

 is left ; but the cell, now a shut cavity, still exists toward the 

 axis of the polypidom. 



" Thus, then, the last external mark of the individual existence 

 of these collected polyps disappears before that life is extinct in 

 the interior, and the most remarkable character of the polypidom 

 is lost without hope of recovery. 



"Eeflecting on the fact we have just noticed, we are naturally 

 led to ask how the nourishment necessary for the support of the 

 secretions on which the progress of consolidation depends, can 

 continue when the cell containing the digestive apparatus of the 

 animal is shut up in this manner. Is it from its neighbors that 

 it receives its nutritive matters, or can it continue to absorb them 

 directly from without through these stony integuments ? The 

 nature of this solid shell seems at first sight to oppose great 

 obstacles to this imbibition, particularly to that which would 

 take place by the free surface of the polypidom, but an experi- 

 ment which is, so to speak, the counterpart of that which has 

 been already detailed, shows that it is otherwise. 



'' On boiling a fragment of the solid polypidom of an Esohara. 

 in a solution of caustic potash, I have extracted the major part 

 of the substance which composes the organized part of its tissue, 

 and I have then seen that the appearance of the polypidom is 

 considerably changed. The external parietes of the cells had 

 become of an almost spongy texture, and its surface, from 

 being simply granular, presented a great number of very distinct 

 pores, which were before concealed by the soft parts with which 

 they were filled. 



" We may understand, then, that the organized tissue of the old 

 polyps finding itself without covering in different points of the 

 external surface of the cells, the absorption may continue to be 

 effected directly from without, although the opening by which 

 the nutritive matters penetrate usually into the digestive cavity 

 is obstructed and obliterated." (From Johnston's History of 

 British Zoophytes.) 



The Opekcula. 



Nearly all the forms in the sub-order Cheilostomata are sup- 

 plied with a chitinous organ for the purpose of closing the mouth 

 of the cell when the animal is retracted. In the fossil Ctclosto- 



