636 Studies in the Theory of Descent. 



not without further evidence be interpreted as the 

 result of the action of a phyletic vital force, but 

 that more probably we had here only an apparent 

 case of new formation, which was in reality but a 

 reversion to a stage formerly in existence. 



If this last investigation removes the only 

 certain observation which could have been ad- 

 duced in favour of the hypothesis of a phyletic 

 vital force, so also do the two former essays show 

 that this hypothesis, at least in the case of insects, 

 must be abandoned as inadeqate. 



The question now arises whether this con- 

 clusion, based on such a limited range of inquiry, 

 can also be applied to the other groups of the 

 organic world without further evidence. 



The supporters of a principle of organic de- 

 velopment will deny this in each individual case, 

 and will demand special proof for each group of 

 organisms ; I believe this position, however, to be 

 incorrect. Here, if anywhere, it appears to me 

 justifiable to apply the conclusions inductively 

 from special cases to general ones, since I cannot 

 at all see why a power of such pre-eminent and 

 fundamental importance as a phyletic vital force 

 should have its activity limited to solitary groups 



A. Milhausenii into A. Salina by diminishing the saltness of 

 the water, have been made by Schmankewitsch (Zeitschrift 

 f. wiss. Zool. xxv. Suppl. 103 and xxix. 429), but the changes 

 which occur hero are much less considerable than in the case of 

 the Axolotl. R. M.] 







