THE ENER GY OF E VOL UTION. 487 



modified by statical agencies its figure may be said to 

 be subject to statogenetic influences. No existing 

 larval form has escaped the influence upon its own 

 shape of a constantly active statical equilibrium of its 

 own substance. There is, therefore, a constant strug- 

 gle going on during development between the phylo- 

 genetic and ontogenetic forces, determining the se- 

 quence and relations of the successive cleavages of the 

 egg and the statical equilibria that obtain amongst its 

 several parts. Statogenetic processes are, therefore, as 

 constant and universal as the phylogenetic and onto- 

 genetic. One may even go so far as to say that possi- 

 bly the relations thus tending to be established by 

 statical conditions may tend to become transmissible 

 as hereditary tendencies. Such indeed is the view up- 

 held by Prof. E. B. Wilson in his remarkable paper on 

 1 The Cell-Lineage of Nereis.' I have myself seen no 

 less than three consecutive recurrences of the same 

 statical conditions in a fish egg, none of which can, 

 for this reason, be definitely proved to be purely onto- 

 genetic. 



''While such phenomena as those of the genesis 

 of the heterocercal or upwardly deflected condition of 

 the axis in the tails of fishes, or the downwardly de- 

 flected condition of the axis in Ichthyosauri are almost 

 purely kinetogenetic, the multiplicity of factors con- 

 cerned, statogenetic as well as ontogenetic and phylo- 

 genetic, must always be considered and each given its 

 due weight and importance in achieving the morpho- 

 genetic result. That there is an absolute conflict be- 

 tween statogeny and kinetogeny on the one hand, and 

 of phylogeny and ontogeny on the other, in the case 

 of the development of the ova of multicellular forms -, 

 admits of no doubt. All metazoa pass through larval J 



