Xo. 50GJ KELPS A XD PEC APITU LATIOX THEORY KM 



Tims the embryogeny will be gradually shortened by 

 the omission of more and more of the superfluous ances- 

 tral stages; and it will tend finally to retain only such 

 stages as are necessary to the attainment of the adult 

 form. It will be noted that this is the view of His, which 

 thus becomes a statement of an inevitable tendency in 

 development, which is very different from a complete law 

 of embryogeny. Though life cycles may approach very 

 closely such a limiting condition, it is doubtful if they 

 would ever completely realize it. 



Besides changes in ontogenies brought about by the 

 cutting off of end stages no longer used there is another 

 source of change. This is secondary adaptation. It is 

 on this point that Montgomery largely makes his case, 

 insisting that organisms are as subject to change in one 

 period of their life cycles as another. In this matter also 

 we must agree that secondary changes are sometimes 

 very evident and conspicuous— probably more so among 

 animals than plants. The total membranes are very fa- 



though they are much modified the fact must not be 

 lost sight of that they are in part at least adaptations 

 of previously existing organs with different functions 

 and not new structures. Not only may an embryo adapt 

 itself to its conditions ; it may simulate other forms ; or 

 interpolate stages; or become otherwise modified as the 

 species undergoes transmutation. Yet the important 

 point to consider is not that a few have done this, but that 

 the great majority have not falsified their heritage be- 

 yond all recognition, that they still persist in spite of 

 changed conditions and secondary adaptation in preserv- 

 ing so many indications of their ancestry. 



Montgomery considers this matter of secondary change 

 so weighty, not because of a great amount of observation 

 brought forth, but for logical reasons. He holds that: 



