526 PRIMARY FACTORS OF ORGANIC EVOLUTION. 



situated between the last thoracic and first pair of ab- 

 dominal legs, which are appended to the seventh 

 euomere. Now in the larva of Nematocarpafilamentaria 

 which bears two pairs of remarkable filamental tuber- 

 cles rolled up at the end, it is certainly very sugges- 

 tive that these are situated on top of the loop made 

 by the caterpillar's body during progression, the first 

 pair arising from the second, and the hinder pair from 

 the fourth abdominal segment. 



" It seems, therefore, that the humps or horns arise 

 from the most prominent portions of the body, at the 

 point where the body is most exposed to external stim- 

 uli ; and the force of this is especially seen in the con- 

 spicuous position of those tubercles which are volun- 

 tarily made to nod or so move as to frighten away 

 other creatures. Perhaps the tendency of these seg- 

 ments to loop or hump up, has had a relation of cause 

 and effect in inducing the hypertrophy of the dermal 

 tissues entering into the composition of the tubercles 

 or horns.' 3 



Prof. W. B. Scott 1 says : "To sum up the results 

 of our examination of certain series of fossil mammals, 

 one sees clearly that transformation, whether in the 

 way of the addition of new parts or the reduction of 

 those already present, acts just as if the direct action 

 of the environment and the habits of the animal were 

 the efficient cause of the change, and any explanation 

 which excludes the direct action of such agencies is 

 confronted by the difficulty of an immense number of 

 the most striking coincidences. ... So far as I can see 

 the theory of determinate variations and of use-inheri- 

 tance, is not antagonistic, but supplementary to nat- 

 ural selection, the latter theory attempting no explana- 



1 American Journal of Morphology, 1891, pp. 395, 398. 



