498 Dr. H. A. Nicholson and Mr. A. H. Foord on 



aspect to the cells (PL XVI. fig. 1 c), interrupting the conti- 

 nuity of their outline and forming hj its free ends two tooth- 

 like projections in the interior of the cell. It will be noticed 

 that the fold is of a lighter colour than the other part of the 

 cell-wall. This lighter portion consists of crystalline calcite 

 of a similar character to that of the matrix or infilling of the 

 cells, though very slightly darker, while the remaining portion 

 of the cell-wall and the walls of the mesopores are composed 

 of a dense, granular, opaque calcite. This difference in the 

 mineral composition in the two parts of the cell-wall must 

 certainly have originated in the living tissues of the organism, 

 because the same phenomenon is met with in species from 

 such widely separated localities as Canada and Westphalia. 



Concerning the morphological significance of the peculiar 

 modification of the cell-wall we have just described, a valuable 

 suggestion has been made to one of the writers by Prof. 

 H. N. Moseley and Mr. G. B. Howes, after examining many 

 .specimens and sections of Fistuli^ora^ to the effect that these 

 structures may have formed a portion of the endo-skeleton 

 supporting in the animal a ciliated groove (siphonoglyphe) 

 similar to that which is found in the stomoda3um of the 

 Alcyonarians*. 



This suggestion seems in our judgment to yield the only 

 explanation which, in the present state of our knowledge, can 

 be afforded in reference to this most interesting question. Some 

 further observations upon it, however, appear to be needful. 



We have seen that the folds in Fistulipora are present only 

 in the autopores (^aw^o^-oo/c^s of the Alcyonarians?) and not 

 in the mesopores [^siphonozooids of the Alcyonarians ?). 

 Their strong development in the former may be explained by 

 supposing that the mesopores, becoming aborted, threw upon 

 the autopores the task of supplying by their strong cilia the 

 circulation of sea-water requisite for the nourishment of the 

 colony. The peculiar condition of the mesopores in Fistulipora 

 lends support to this view, as the close vesiculose tabulation 

 which characterizes them would be difficult of explanation 

 upon any other hypothesis. 



With reference to the (assumed) occurrence of such a 

 strongly marked ciliated groove in the autopores of the Fis- 

 tuUpora-colonj it may be alleged that this is a somewhat 

 rare condition to meet with in living Alcyonarians ,• but it is 

 not altogether wanting in that group, for we find in the genus 

 Sarcophyton (a dimorphic form) that the autozooids possess a 



* Sydney J. Hickson, " On the Ciliated Groove (Siplionoglyplie) of the 

 Stomodfeum of the Alcyonarians," Phil. Trans. Royal Soc. part iii. 1883. 



