126 ORIGIN OF SOMATIC 



the stimulus suddenly ceases. The bone also begins 

 to die when the skin and periosteum is stripped off, 

 and the hormone from this also ceases to be pro- 

 duced. 



The annual shedding and recrescence of the 

 antler, however, is only to be understood in connexion 

 with the effect of the testicular hormone. According 

 to my theory there are two hormone actions, the 

 centripetal from the hypertrophied tissue to the 

 corresponding factor in the gametocytes, and the 

 centrifugal from the testis to the tissue of the antler 

 or other organ concerned. The reason why the 

 somatic sexual character does not develop until the 

 time of puberty, and develops again each breeding 

 season in such cases as antlers, is that the original 

 hypertrophy due to external stimulation occurred 

 only when the testicular hormone was circulating in 

 the blood. The factor in the gametocytes then was 

 in each generation acted upon by both hormones, 

 and we must suppose that in some way the result 

 was produced that the hereditary development of the 

 antler in the soma only took place when the testicular 

 hormone was present. It is to be remembered that 

 we are unable at present to form a clear conception 

 of the process of development, to understand how 

 the simple fertilised ovum is able by cell-division 

 and differentiation to develop into a complicated 

 organism with organs and characters predetermined 

 in the single cell which constitutes the ovum. If we 

 accept the idea that characters are represented by 

 particular parts of the chromosomes, according to 

 Morgan's scheme, our theory of development is the 

 modern form of the theory of preformation. When 

 in the course of development the cells of the head 



