621 



number contained in the whole section was determined. Three such in- 

 dependent processes for stage 1 gave, for instance, 85 755, 83 585 and 

 81 200, the average being 83 514. When we consider the immense 

 difference got in the different specimens, these numbers are quite near 

 enough to show the general reduction which occurs. 



3) The flexorpro fundus digitorum, with which is associated 

 the flexor longus pollicis of the tame rat at 2 days old contained 

 3 020 and at 47 days old 2 275 fibres. 



The results got in this preliminary investigation into the post- 

 embryonal changes occurring in muscle fibre are weighty enough to 

 justify immediate publication. I reserve for a future paper a more 

 detailed examination of intermediate stages and an enquiry into how 

 far the result may be modified by sex, variation, habit, feeding and 

 breeding. 



In my paper on post-embryonal development approached from a 

 statistical Study of the Incisor Teeth of the Horse ^), I showed that 

 bone passed during life through processes of adjustment which could 

 only be paralleled in pathological conditions. It was absorbed in 

 response to pressure and deposited where pressure was removed. In 

 muscle we have evidently similar processes going on. It is quite evident 

 that the fibres which assert their position and those which are squeezed 

 out of existence were not predestined to these fates by the evolution 

 of determinants present in the ovum. The lucky fibres get into a 

 better relationship with the nutritive supply through having a more 

 telling position for taking part in the activity of the muscle. They 

 increase and increase and their more unlucky neighbours have to 

 give place to them. We have here indeed a survival of the fittest in 

 a competition as keen as that say among the plants in a pasture or 

 the branches of a tree. 



8 July 1898. 



1) The Veterinarian, 1897. 



