STUDIES ON THE DYNAMICS OF MORPHOGENESIS 269 



it also becomes clear that in the products of sexual reproduction 

 in the higher animals heredity appears in its most complex form 

 and under conditions which render analysis almost impossible. 

 Doubtless we can establish rules which will have a greater or 

 less empirical value, but the conditions of sexual reproduction 

 are such as to make the problem one of the most if not the most 

 difficult and inaccessible with which the biologist is concerned. 



In the simpler forms of asexual reproduction in the simpler 

 organisms, there exists the possibility of a greater degree of control 

 of the conditions of reproduction and development, and therefore 

 of further insight into the nature of inheritance. And finally 

 in the experimental reproductions, i e., the processes of reconsti- 

 tutional regulation following the physiological or physical iso- 

 lation of parts of the organism, there exist still further possibili- 

 ties of control and analysis, which are not present in either 

 asexual or sexual reproduction in nature. I believe there is 

 much to be learned from these simpler forms of reproduction 

 that the breeding and crossing of sexual forms can never teach us : 

 I believe further that our hypotheses and theories of heredity 

 must sooner or later take as their starting point the simplest 

 phenomena of reproduction and development, not the most com- 

 plex. 



I am well aware that objections to this point of view may be 

 raised. It will doubtless be maintained by some that inher- 

 itance from pieces of the soma is quite a different matter from 

 inheritance through the germ plasm. Such objections are based 

 merely on theoretical grounds and my reply is simply that ' germ 

 plasm' exists wherever reproduction occurs. I believe we are 

 logically bound to extend the conception of heredity to every 

 form of reproduction. Moreover, there is much evidence, which 

 I hope to discuss at another time, in support of the view that 

 the sex cells are primarily just as much a physiological part of 

 the individual organism as other organs and that they undergo 

 sooner or later in the course of their differentiation a process of 

 physiological isolation. Some of this evidence I have presented 

 briefly in other papers (Child, '11a, pp. 81-88 'lib). In short 

 there are no facts which contradict, and there are many which 



