Henriksen, A Functional view of Development. 23 



dependent on the number of cats. The parts of the orgänism are 

 what they are because of their relation of other parts in their 

 common object to establish the equilibrium of the species. 



No more can we say it lies within the structure of the 

 chromosomes becanse our most careful plant and animal cytologists 

 have shown that in the cleavage division part of the chromation 

 substance in offen lost. All we can say is that the egg possesses 

 the vital growth energy as a common factor and an Organization 

 which enables it to start progressive relations towards the deve- 

 lopment of the adult form, in establishing this equilibrium. 



Let us first apply this to individual cells and later to the 

 embryology to see whether experimental methods have approved 

 of the above hypothesis or whether we have to assume a structural 

 basis of heredity. 



Front this view of development the multiplication, the asexual 

 reproduction, among the protozoa, to be understood only in a 

 general way, is due to the fact that the process of growth has 

 caused a state of equilibrium within the cell and by divison it is 

 restored. 



We know already from experiments that non-nucleated frag- 

 ments of a cell may be fertilized by a sperm, and that an egg may 

 be stimulated to develop by artificial means, in both cases a per- 

 fect larva results but of only half the size of the normal one. 

 These experiments show that no fusion of two muclei are neces- 

 sary to start embryologic development, but that it takes a Stimulus 

 of some kind to start it to activity and cause a flowing of the 

 cytoplasm which results in a state of inequilibrium whereby cell 

 division is brought about. We will now see whether we have any 

 direct evidence that such a relation exists between the parts of 

 the egg, and we could choose no better illustration for this than 

 Boveri's remarkable experiments on dispermic, double fertilized 

 eggs from which he concludes that it is not only the number of 

 chromosomes which is the important factor but the Organization 

 the functional capacity of these are of absolute importance for 

 normal development. That the relations are disturbed when even 

 only a part of the cytoplasm is removed from the egg has been 

 shown by Prof. E. B. Wilson, Driesch and Morgan especially 

 on the eggs of the ctenophores so as to give rise to a defected 

 larva but nevertheless it tends to establish the equilibrium by 

 healing the wound. This shows that the removal of the cytoplasm 

 from one side of the egg disturbs the development of the cells 

 which arise from that side but it must here be emphasized that 

 no attempt has been made to dispute that we can trace the various 

 parts of the larva back to certain blastomeres as has been shown 

 in numerous forms only that it is not predetermined excej)t by its 

 relations to other parts. Another beautiful illustration of the fine 

 adjustment within the egg is shown by the alternating dexio — and 

 laeo — tropic position of the spindle as shown in many eggs of 

 determinate cleavage. 



