On the Mechanical Conception of Nature. 635 



reason for inferring the existence of some still 

 unknown modifying cause lying concealed in the 

 organism. In this region of the marking and 

 colouring of caterpillars, the assumption of a 

 phyletic vital force had to be abandoned, as being 

 superfluous for the explanation of the facts. 



In the second essay the attempt was next made 

 with reference to double form-relationship, as pre- 

 sented for observation in metamorphic insects, to 

 draw conclusions as to the causes of the trans- 

 formations. It appeared here that form- and 

 blood-relationship do not always coincide, since 

 the larvae of a species, genus, or family, &c., may 

 show quite different form-relationships to their 

 imagines. These facts alone told very decisively 

 against the existence of an internal developmental 

 power, so that the latter had likewise to be set 

 aside by the method of elimination, since the 

 observed incongruences as well as the con- 

 gruences of form -relationship, found sufficient 

 explanation in the action of the environment on 

 the organism. 



This investigation thus also led to the denial of 

 a phyletic vital force. 



In the third essay I finally sought to prove 

 that the only case of transformation of one species 

 into another at present actually observed 1 , could 



1 [Some experiments on the transformation of the Crustacean 

 Artemia Salina into A. Afilhausfnii by gradually increasing 

 the saltness of the water, and conversely, the transformation of 



T t 



