PROCESS OF REPRODUCTION IN ORGANISMS. 2Q 



In this case then the same region of the body is concerned in 

 both asexual and sexual reproduction and the early stages of 

 asexual buds and of gonads are similar. The reproductive cells 

 of the younger, less highly differentiated animal are themselves 

 less highly differentiated and so develop asexually into new 

 medusae, while the reproductive cells which arise when the 

 animal is older and more highly differentiated develop into the 

 highly differentiated gametes, which require fertilization. 



In the higher organisms, where the structural features are more 

 stable and the capacity for dedifferentiation and rejuvenescence 

 is limited asexual reproduction disappears and sexual reproduc- 

 tion remains as the only method of reproduction. In many of 

 these forms, however, the absence of asexual reproduction in the 

 earlier stages is due, not to the absence of capacity for reaction 

 to isolation, i. e., for regulation, but to the fact that under 

 natural conditions parts do not become physiologically isolated. 

 Experiment has shown, for example, that in the eggs and embryos 

 of various vertebrates isolation of parts is followed by more or 

 less complete regulation and the occasional occurrence of identical 

 twins in man, as well as the occurrence of polyembryony in the 

 armadillo as a natural phenomenon (Newman and Patterson, 

 '09, '10), indicate that even in the mammals the earlier stages 

 still retain a high capacity for asexual reproduccion. It is not 

 impossible that we may be able at some time with proper tech- 

 nique to induce asexual reproduction, even in parts of the older 

 vertebrate organism. 



In plants, likewise, sexual reproduction is characteristic of the 

 old organism with a relatively low rate of metabolism and it can 

 often be induced by bringing the plant under condi lions which 

 decrease metabolism. The fact that in the lower plants the 

 gametophyte is usually simpler morphologically than the sporo- 

 phyte does not, I believe, constitute a real exception to the 

 general law. The sporophyte is a form in which most of the 

 cells become at an early stage so highly differentiated that they 

 are entirely excluded under ordinary conditions from the function 

 of reproduction. Only those parts which remain in a relatively 

 primitive condition or which differentiate relatively slowly play a 

 part in reproduction. These parts are, so far as we can judge, 



