GENERA OF CH.ETETID.E AND MONTICULIPORID.E. 285 



their mouths to assume a circular or oval shape, and to project 

 above the general surface. Lastly, the fossil is said to change 

 into a Monticulipora by the development of regular " monti- 

 cules," which are " arranged in quincunx, and formed at the 

 points where seven or eight large cells are clustered." 



In the preceding I have endeavoured to give a faithful 

 account of the views which Dr Lindstrom has published as 

 to the development of the MonticuliporcE, and upon which 

 he, in large part, bases his view that the fossils of this genus 

 are really Polyzoa. Not having had the opportunity of per- 

 sonally examining the specimens upon which his views are 

 based, it would be presumption on my part were I to impugn 

 the accuracy of the description which he has given of the 

 phenomena which he has observed — the more so as his justly 

 deserved reputation is a guarantee that he has not arrived 

 at the conclusions in question without sufficient consideration. 

 At the same time, I regret to find myself in the meanwhile 

 unable to accept these conclusions ; and though I cannot 

 here enter into the subject at length, I may just briefly 

 indicate the principal reasons which lead me to dissent from 

 the views of such a high authority upon this and kindred 

 questions. In the first place, then, it is clear that the study 

 of the development of a fossil organism is attended with 

 difficulties much more serious than those which are incidental 

 to a similar investigation in the case of a living animal ; since 

 in the latter it is generally possible to trace the actual tran- 

 sition from one stage of growth to another. This, by the 

 nature of the case, is rarely — one might almost say never — pos- 

 sible in the case of a fossil. It is true that in the passage of 

 what he has termed the " Fistiilipora stage" to the " Thecoste- 

 gites stage," Dr Lindstrom states that he has actually seen the 

 same specimen exhibiting the characters of both stages in dif- 

 ferent parts of its skeleton. Still the passage between the two 

 stages just referred to is a comparatively small step to make, 

 and it does not aff"ect the fact that Dr Lindstrom has not 

 observed — so far as I am able to understand his very clear 



