88 PRIMITIVE FORMS OF LIFE 



to claim as much for the use or disuse of every organ, at least 

 it cannot be denied that exercise does expand the muscles and 

 create new habits. 



The organism possesses within itself the various causes for 

 those chemical modifications which are so important. Every 

 cell in the body, from the very fact that it feeds and is active, 

 exudes around it substances which then become diffused 

 throughout the entire body and consequently make their 

 activity felt in varying degrees throughout the whole. Apart 

 from the modifications that may arise from the mere mode of 

 functioning, every organ, by the very act of functioning, tends 

 to modify the whole organism in some particular manner. 

 The substances by means of which it acts unquestionably 

 possess certain elective affinities for some particular element, 

 but, in the case of animals, they may have a general influence 

 upon the organism either by direct diffusions or by way of the 

 nervous system. For instance, they may augment or diminish 

 its size, as in the case of acromegaly due to disturbance of the 

 function of the pituitary body. They may act also upon a 

 particular tissue or organ, or on some particular system or 

 apparatus, thereby exercising a local influence changing the 

 relative proportions of organs, thus modifying the external 

 form of the body. Armand Gautier x has shown that the 

 morphological characters of different varieties of vines corre- 

 spond to modifications in the chemical composition of their 

 pigments, which, although all belonging to the same chemical 

 type, differ in the number and the composition of the radicals 

 constituting them. The reproductive organs are to be reckoned 

 among those in which chemical action is most vigorous. 

 We know, for instance, what extensive modifications 

 they may bring about in reproductive leaves and the 

 leaves which surround them — petals, sepals, bracts, and 

 in Poinsetia, even in a certain number of its ordinary 

 leaves. Analogous modifications have been observed on 

 the reproductive rami of hydroid polyps, 2 and the gay 

 " bridal dress " which many Worms, Fish, Batrachians, 

 Reptiles, and Birds put on at the breeding season has 

 often been described. The coincidence between the formation 



1 LXVI. 



2 Corbullidae of Aglaoahenia, phylactocarps of Lytocarpus, Medusas of 

 Campularia and gymnoblastic Hydras. 



