No. 561] THE Xl.XE-BAXDED ARMADILLO 531 



the controlling part of the system, say the animal pole 

 of the blastodermic vesicle, is liahle to physiological iso- 

 lation of parts at certain distances from the dominanl 

 region. "When such isolation of parts occurs new centers 

 of control arise, which produce buds capable of estab- 

 lishing whole new systems like the original. Thus in the 

 particular case under discussion the rate of metabolism 

 of the whole vesicle is lowered by parasitism to such an 

 extent that the dominant growth center of the system no 

 longer is able to hold the various subsidiary growth 

 regions under control, and new centers of control arise at 

 points determined by secondary pressures exercised by 

 the uterine grooves, as explained above. Further com- 

 plexities in development are of the nature of adjust- 

 ments of four separate fetuses compelled to carry on 

 growth and differentiation within a common chorion 

 which had already been established before physiological 

 isolation of the four embryonic rudiments had taken 

 place. According to current theories, reproduction is a 



