560 SCIENCE PROGRESS 



the influence that should control it, and stung into activity 

 by a stimulus which, judging from the analogy of the race, 

 is in all probability a chemical one. 



The testis, it may be remarked, the complementary half 

 of the primitive germ organ, does not retain this power in 

 anything like the same degree as the ovary, probably because 

 it has become more highly specialised. 



Direct Reproduction from Somatic Cells 



All that is true of the origin of the tumours that grow 

 from germ cells is equally true of those that grow from somatic 

 ones. In both the formation of tumour buds is due to a 

 sudden awakening of the primitive power of direct repro- 

 duction innate in the tissues, or rather of all that is left of it. 



In the earliest days of existence the function of reproduction 

 is shared by all the cells of the organism alike. When, owing 

 to increase in size, labour has to be divided this function is 

 assigned to one particular group, known henceforth as germ 

 cells. All reproduction is direct until the bi-sexual method is 

 developed. Then the direct method gradually ceases to be 

 used, and from being employed so seldom, falls into the back- 

 ground and all but dies out. 



The same thing occurs with the somatic cells. At the 

 beginning their power of direct reproduction is equal in all 

 respects to that of the germ cells. They, too, can give off 

 buds which are capable of developing into organisms like 

 themselves. But when the division of labour begins, and 

 somatic cells have all to undertake different duties, they 

 surrender this one to the germ cells, and never carrying it out 

 themselves they lose the power of doing so. 



They do not lose it all at once. The power of direct repro- 

 duction diminishes step by step as organisation advances. 

 The process can be traced as well in the history of the race 

 as in that of the individual. In the simplest forms of animal 

 life and in the earliest days of those that are more highly 

 organised the power the somatic cells enjoy is almost un- 

 limited. Many of the ccelenterata, for instance, can regener- 

 ate themselves from fragments taken from any part of the 

 original body, and buds capable of developing into imperfect 

 foetuses can grow from different portions of the embryo even 



