THE (;erm-plasm S^ 



determinants whicli were formerly present must have dis- 

 appeared entirely from the id of germ-plasm, and the remainder 

 must have lost the power of multiplication to a greater extent 

 than has occurred in the case of the wing oi Apte?yx. 



We know, however, that even in such animals as snakes, in 

 which the extremities have in most cases disappeared com- 

 pletely in previous geological periods, the rudiments of the 

 limbs arise in the form of ' muscle-buds ' in the earlier stages of 

 development, and then disappear very shortly afterwards.* 

 This fact may be expressed in terms of the idioplasm as 

 follows: — the power of multiplication in the small remnant of 

 the group of determinants of the extremity which still exists in 

 the id of germ-plasm, has decreased so considerably that it only 

 suffices for these early embryonic stages. The youngest deter- 

 minants, and consequently the most recent hereditary structures, 

 are the first to disappear, the loss of the older ones taking place 

 gradually, until even the oldest of all are no longer present. 

 This must be due to the manner in which the deter- 

 minants increase, although the actual connection between the 

 two phenomena is not apparent. It may perhaps be traced to 

 the fact that those determinants which are the youngest phy- 

 letically are destined for the latest ontogenetic stages, in which 

 only therefore they become ' ripe,' and undergo disintegration 

 into biophors. If then, their power of multiplication decreases 

 considerably during the process of degeneration, the number of 

 determinants required for the control of any particular group of 

 cells will not be reached, nor will the determinants even become 

 ripe. Although still present, they are unable to exert any in- 

 fluence ; whereas the determinants of the older phyletic stages 

 which are still passed through, ripen in the earlier stages of 

 ontogeny. 



The process of degeneration of an organ may be represented 

 as depending on the fact that the determinants first become 

 changed in such a manner as to cause a decrease in tlieir power 

 of multiplication, and this then leads to a very gradual reduction 

 affecting an increasing number of determinants belonging to 

 the group in question. At the same time, the power of mul- 



* Cf. J. van Bemmelen, ' Over den oorsprong von de vorsle lede- 

 maten en de tongspieren bij Reptilen.' Kon. Akademie de Wetenschappen 

 te Amsterdam, 30th June 1888. 



