TRANSFORMISM 239 



excretory substances, and that these stimulate certain 

 cerebral centres, which in turn accelerate the rate of 

 action of the heart and respiratory organs. An in- 

 creased flow of nutritive matter and oxygen then 

 traverses the blood-vessels in the muscles of the 

 shoulders and arms, and the latter grow. Probably 

 processes of this kind do occur, but to say that they 

 do is not to give any real explanation of the hyper- 

 trophy of the musculature of the man's body, for what 

 essentially occurs is the division of the nuclei and the 

 formation of new muscle fibres. How precisely does 

 an increased supply of nutritive matter cause these 

 nuclei to divide and grow ? This is a relatively simple 

 example of the adaptability of a single tissue-system 

 to a change in the general bodily activity, that is to 

 say it is a variation of structure induced by an environ- 

 mental change. 



In most cases, however, the variations of structure 

 that form the starting-points of transmutation processes 

 cannot clearly be related to environmental changes. 

 Some fishes produce very great numbers of ova in 

 single broods — a female ling, for instance, is said to 

 spawn annually some eighteen millions of eggs. If we 

 examine these ova we shall find that there is consider- 

 able variation in the diameter and in other measureable 

 characters. We may attempt to correlate these devia- 

 tions from the mean characters with environmental 

 differences. All the eggs " mature," that is, they 

 absorb water and swell, while various parts, such as 

 the yolk, undergo chemical changes, during the month 

 or so before the fish spawns. This process of matura- 

 tion takes place in the closed ovarian sac ; and the 

 eggs lie practically free in this sac, and are bathed in a 

 fluid which exudes from the blood-vessels in its walls. 

 It may indeed be the case that there are variations in 



