MATERIALS FOR A MONOGRAPH OF THE ASCONS. 563 



adaptation to the needs of the whole organism^ resulting in 

 the form best suited for the function which the sclerite has to 

 perform — the function, namely, of supporting the tissues in the 

 manner required by their structure and arrangement in the 

 primitive forms in which the spicules first arose. 



In explaining the main types of calcareous spicules by 

 adaptation, we are referring them to a very wide-spread and 

 universal category of structures characteristic of living beings. 

 There is probably no living organism which does not possess 

 some special features, owing their characteristics or even their ex- 

 istence to the fact that they are of utility to the organism in its 

 efforts to maintain and perpetuate its existence in the way in 

 which its environment necessitates. If now it be asked how 

 this process of adaptation came about, Ave find ourselves con- 

 fronted with one of the most important and fundamental ques- 

 tions of evolution. The most commonly received explanation 

 of adaptation is that put forward by Darwin — namely, that it 

 is due to the natural selection of favorable varieties in the 

 struggle for existence, resulting in the survival of the fittest 

 types and the gradual elimination of the less perfectly 

 adapted. 



Very recently, however, Delage (1895) has put forward a 

 very different view. Natural selection, according to him, is 

 not a factor of progress in evolution, but one which tends to 

 maintain the fixity of the species by elimination of harmful 

 variations. Adaptation, we are told, is the rock upon which 

 both Darwinian and Lamarckian hypotheses founder, since 

 natural selection is an inadequate explanation, and acquired 

 characters are not inherited (p. 839). There is no phylo- 

 genetic adaptation ; that is to say, species are not adapted to 

 their mode of life, but it is the individual which becomes 

 adapted by its reaction to its environment — " auto-regula- 

 tion " (p. 828). "Phylogeny creates organs without regard to 

 function; ontogeny . . . adapts them to the necessary func- 

 tions :" in other words, " in phylogeny it is the organ which 

 makes the function ; in ontogeny it is the function which makes 

 the organ " (p. 831). The cause of this ontogenetic adapta- 



