96 Mr. E. Hitchcock on the Causes of Variation. 



abundant. It may be conceived tliat if 0. complanata were 

 placed in situations less favourable as regards food it would 

 die of starvation, owing to the quantity of inner sarcode 

 requiring nourishment, while 0. tenuissima needs only more 

 favourable conditions as regards food and, perhaps, tempera- 

 ture to become as highly complex in structure as the last- 

 mentioned species. As a further proof of the influence of 

 environment leading to changes which cannot be regarded as 

 special adaptations, in the usual meaning of the word, the 

 forms of Of compla7iata found on Fiji reef are especially 

 characterized by thick plicated margins, as though growth 

 proceeded with too great rapidity to produce symmetrical 

 disks, and these forms are associated with the largest repre- 

 sentatives of the species. 



The distinction above referred to seems an important one, 

 which, if it lias already been recognized, has not been promi- 

 nently brought forward in the writings with which I am 

 familiar. Before the Biological Society the subject was 

 briefly considered in the following Avords : — 



" liegarding the subject from this point of view, we are 

 led to examine more closely the relations between the spiral 

 and the cyclical methods of growth. Their intimate relation 

 is only noticeable when we observe how one has been derived 

 from the other. When the spiral growth of Orhiculina pro- 

 duces a complete circular disk, further spiral growth becomes 

 impossible ; and if we concede that the extrusion of the 

 sarcode to form successive chambcrlets is due to nutrition and 

 growth, the cyclical plan then becomes a necessity. In this 

 way it may be supposed cyclical growth originated, purely a 

 result of nutrition, not by adaptation to environment, but as 

 a result of it ; not because such growth is or ever was better 

 adapted to the conditions of life. 



" We find here a steady course of variation a result of 

 physiological ])rocesses, independent of those external causes 

 to which Ave are accustomed to attribute such changes. These 

 variations, as successively produced, have been perpetuated 

 through inheritance, until the plan of growth has, in some 

 species, totally changed. Herein, therefore, we may find an 

 indication of how the plan of growth originated, and a sugges- 

 tion that the inscrutable laws wliich govern the progress of 

 evolution may each have beginnings equally simple, and not 

 beyond the range of human insight to discover. Evolution in 

 this case seems not to be a result of a definite plan of growth, 

 but the plan of growth is the result of physiological pro- 

 cesses. However great and important the influences of 

 environment and selection may have been in the production 



