Henri ksen, A Functional view of Development. 35 



condition and that developing organisms arc extremely sensitive to 

 external Stimuli and that this sensitiveness varies greatly among 

 the different kind of animals. 



To show the more complex cases of the relations between 

 cells and groups of cells, brought about by nervous action we 

 could take numerous illustrations but I shall give only the fact 

 that if the nerve is severed in a developing limb it immediately 

 stops to develop and degenerates. Herbst described a case of a 

 call' where a great part of the spinal cord did not develop and as 

 a result the nerves were absent in many parts and inhibited the 

 muscles in their development. Such an Illustration shows clearly 

 the importance of Innervation in establishing the equilibrium of the 

 species. 



We will now consider as briefly as possible regeneration of 

 lost parts from our point of view, but it will become clear that 

 the difference of this and those cases just discussed are rather of 

 degree than kind. If we take illustrations from the lower animals 

 we may cut them to pieces, as we did when separating the blasto- 

 meres of earlier cleavages, and they will develop into adult forms 

 but as we go up in the animal scale this power is completely lost 

 as among the higher vertebrates. Of regeneration among larval 

 form Driesch gives an interesting case where he bisected the 

 gastrula of Sphaerechinus through the equator so that each half 

 contained both ectoderm and endoderm. Both halves heal and 

 from typical gastrula in which the enteron differentiates itself into 

 three typical regions (fore, middle and hind gut) correctly propor- 

 tionated, though only half the normal size. Can we possibly find 

 a more beautiful illustration of the principles given above and 

 against the preformation theory? To take up the discussion of 

 regeneration among the higher forms is impossible in the time 

 allowed here; so I can do no better than quote Prof. C. M. Childs 

 conclusion to an article on regeneration where he says: "Experi- 

 ments have shown that formative factors are many and various and 

 generalizations from a single group of characters are unsafe . . . 

 All complex activities of which organisms are capable are 'formative 

 factors' when we can view all of these in their complex relations 

 and know the parts which each play, then and only then shall we 

 'understand f organic form. The relations between form and here- 

 dity has never been satisfactorily determined. With the advance 

 in our knowledge the fact becomes more and more evident that 

 an organism is not merely a complex of structural elements ready 

 made by heredity for certäin functional activities, but rather a 

 complex of activities in consequence of which morphological struc- 

 ture develop. Physical and chemical structures of protoplasm 

 must not be confused with morphological structure. As regards 

 the individual the former represents capacities for activity in the 

 broader sense, form in the morphological sense is the combined 

 result of this activity and the environment external and internal. 

 According to this view it is the functional capacity that is inherited 



