OTHER THEORIES OF SPECIES-FORMING. 227 



and have beep ever since our practical giving up of the vital prin- 

 ciple notion, making steady progress in the explanation of life- 

 forms and life-functions on strictly mechanical and physico-chemical 

 grounds. While we have by no means explained all life attributes 

 in this way, Biitschli holds that our progress has been such as to 

 make no demand for the introduction as yet of a new vital principle 

 under a pseudo-scientific guise. 



Other neo-Vitalists. of whom G. Wolff is a type, lay chief stress 

 on the inexplicableness of the Zweckmassigkeit in organisms by 

 any of the known biological facts and factors, and see in the deter- 

 mination or very existence of this Zweckmassigkeit the chief revela- 

 tion of a vital factor, wholly distinct from anything found in the 

 inorganic world. Wolff's argument is clever and suggestive, and 

 brings home to one strongly the indissoluble relationship between 

 living matter and its adaptivity. In its fundamental character life 

 is adaptivity : the indispensable relation between living matter and 

 the rest of nature is the pliability, the adaptiveness of the living 

 matter. "Die sweckmassige Anpassung ist das, was den Organis- 

 mus sum Organismus macht, was sich uns als das eigentlichste 

 Wesen des Lebendigcn darstellt. Wir konnen uns keinen Organis- 

 mus denken ohne dieses Charaktcristikum. . . . Und wir erkennen 

 dass jede Erklarung, welche das Leben voraussetzt, jede postvi- 

 tale Erklarung der organischen Zweckmassigkeit, in jedem 

 Falle voraussetzt was sie erklaren will ; wir erkennen dass die 

 Erklarung der Zweckmassigkeit mit der Erklarung des Lebens 

 zusammenf alien muss." 



But perhaps there is a difference between the plastic response of 

 protoplasm to the varying conditions of oxygen, food, temperature, 

 etc., about it, so that within certain limits of external versatility it 

 still lives, and that extraordinary specialisation of fitness which we 

 see exhibited by a parasitic Sacculina with relation to its crab 

 host. And believers in natural selection hold that it is exactly one 

 of the chief glories of selection that it does explain this highly 

 specialised fitness. More than that, closer examination of the 

 phenomena of organic Nature reveals many examples of an unfit- 

 ness, which certainly ought not to exist if there is a special vital 

 principle responsible for fitness throughout the organic kingdom. 

 There is a moth common with us here in California, by name 

 Phryganidia calif ornica, whose larvae live on the leaves of the oak- 

 trees. Two generations appear each year. The eggs for the first 

 brood of caterpillars are laid in spring by the moths on the leaves 

 of the live-oaks and also of the white-oaks. The larvae soon hatch, 

 feed through the summer on the leaves, and in September pupate, 

 the moths appearing in October. These moths now proceed to lay 



