INDIVIDUATION AND REPRODUCTION 231 



undoubtedly a factor in determining the limits of the individual in 

 at least some mammals, for Patterson ('13) has shown that the 

 four embryos of the nine-banded armadillo are the result of agamic 

 reproduction, of a process of budding of the primarily single embryo, 

 and suggests that duplicate twins and double monsters may arise 

 in the same manner. 



There can be no doubt that during the course of individual 

 development a greater or less degree of extension of dominance 

 occurs as the paths of transmission develop. In the early embry- 

 onic stages the influence of the dominant region extends only a 

 short distance, but, particularly in organisms where a nervous 

 system develops, transmission of impulses to greater distances 

 becomes possible as development proceeds. Consequently the 

 size of the individual may increase during development, in many 

 cases very greatly, without physiological isolation of any part and 

 so without agamic reproduction. 



If the control of the dominant over the subordinate parts in the 

 individual is accomplished by means of transmitted impulses or 

 changes which show a decrement with transmission and a limit of 

 effectiveness, then physiological isolation of a part may be brought 

 about in four different ways (Child, 'na). First, physiological 

 isolation may result from increase in size to or beyond the limit of 

 dominance. Many of the phenomena of budding, fission, etc., 

 which occur in consequence of growth, both in plants and in animals, 

 are examples. 



Secondly, physiological isolation may result from a decrease 

 in the limit of dominance, which in turn is the consequence of a 

 decrease in rate of metabolism in the dominant part. It is a well- 

 known fact that many plants give rise to buds or other reproductive 

 bodies under conditions unfavorable to metabolic activity, and 

 while this form of reproduction has often been regarded teleo- 

 logically as in some sense an attempt of the plant to save its own 

 life, it is undoubtedly to be interpreted as the result of a decrease 

 in the limit of dominance. The formation of new buds in plants 

 in consequence of the removal or inhibition of metabolism of the 

 dominant region, the vegetative tip, are likewise reproductive 

 processes which belong to this category. In the lower animals also 



