THEOR V OF DETERMINANTS 449 



restricted, there is a much more useful retention, at spots Hable 

 to injury, of local contingents of " organ-forming units " which 

 can replace lost parts. 



Difficulties. — i. If definite determinants are distributed in 

 development as the number of unit-areas or cells increases, 

 how is it that an isolated group of cells, cut off from a begonia- 

 leaf, a potato-tuber, a hydra-polyp, a sea-anemone, a simple 

 worm, may in appropriate conditions grow into an entire organ- 

 ism ? It must be noted, in the first place, that this capacity 

 is more or less restricted to relatively simple organisms. In 

 the second place, the theoretical answer is that in such cases 

 the cells retain a representation of the whole germ-plasm in an 

 inactive state, though each one of them is differentiated under 

 the control of a particular set of determinants. 



2. A man has a peculiar " crooked nose " and his son has the 

 like. Are we to suppose that the inheritance includes " crooked 

 nose "-determinants ? Weismann would say " emphatically 

 not." A large number of different kinds of determinants are 

 concerned in the up-building of the nose, and they work co- 

 operatively towards a general result. There may be some 

 slight peculiarity in those that contribute, let us say, to the 

 cartilage of the nose, and this peculiarity may, in the course of 

 the co-operative development, lead to a crooked nose as the 

 result of some inequality of pressure during the early formative 

 period. The results of experimental embryology show clearly 

 that the behaviour of particular cells in development is not 

 absolutely stereotyped ; they will do their best, as it were, to 

 work out a constant result, but if this is interfered with environ- 

 mentally they will do something else. At the same time, it 

 is very interesting that abnormal larvae — e.g. the so-called 

 Lithium-larvae of sea-urchins — have a remarkable power of 

 righting themselves when they are relieved from the disturbing 

 influence of the abnormal environment. 



Objections to the Theory of Determinants. — Some biologists 



29 



