806 ANATOMY OF VERTEBRATES. 



superadded cerebral mass for true sensation rigorously fix the 

 limits of volitional faculties. 



We pass then to considerations of the ' ambient medium ' and 

 9 natural selection.' We have no evidence that the fabricators of 

 the coral-reef of Wenlock-edge, or of those skirting the Cambrian 

 slates and Devonshire ( killas,' or of those in the lofty limestone 

 cliffs of Cheddar, worked in an ocean otherwise constituted than 

 the present. What conceivable character of sea or of the air 

 dissolved or diffused therein could have changed the loose aggre- 

 gation of the individuals of composite Rugosa into the close com- 

 bination, with intercommunicating pores, of those of the composite 

 Tabulata ? Or what possible external influence could have 

 transmuted the comparatively simple massive mode of growth or 

 deposition of carbonate of lime common to both Rugosa and Tabu- 

 lata into the light and complex character of the polyparies of most 

 existing lamelliferous Anthozoa ? In the first mode the old polype- 

 cell is successively partitioned off from the one in occupation by 

 floor after floor crossing the cavity : in the other, radiating ver- 

 tical partitions alone occupy the deserted cell and extend uninter- 

 ruptedly from its bottom or beginning to the superficial inhabited 

 chamber. The quadripartite pattern of the plaited cup of the 

 palaeozoic coral has changed into the sexpartite disposition of the 

 radiating lamellae of the polype-cells of tertiary and modern corals. 

 But personifying the fact of such transmutations by the term 

 6 natural selection ' gives no more insight into the manner of the 

 operations than we learn of that of the budding out of a new leg 

 in a maimed newt, by being told that it is done by the ( nisus 

 formativus ' or by ( pangenesis ' ! Even were there evidence of 

 changes in the composition of the atmosphere, their ( modus ope- 

 randi ' in effecting such structural differences would not be more 

 conceivable. 



I do not believe that a sexpartite type of coral was miracu- 

 lously created to supersede a quadripartite one. If the grounds 

 are good for admitting the continuous operation of a secondary 

 cause of the specific forms of Vertebrate life, a fortiori it is ad- 

 missible in the lower sphere of Radiate life. It is consistent with 

 facts that a quadripartite coral might bud out, or otherwise 

 generate, a variety with a greater number of radiating laminae. 

 Some varieties, like those expressed by the modern generic terms 

 Porites, Millepora, especially the M. complanata, with its strong 

 vertical plates, were better adapted to bear the brunt of the 

 breakers, and flourish in the surf, under the protection of the 

 coating Nullipore. But to how small an exception is this rela- 



