332 University of California Publications. [ ZooLocy 
govern its behavior without being necessarily a part of it. These 
conditions are probably chemical in nature, intimately con- 
cerned with the metabolism. A destruction or addition of sub- 
stance or substances in the course of the development is readily 
conceivable as the efficient cause of the structural modification. 
The relation between internal and external conditions is under 
consideration. 
The resemblance of the phenomena of colonial differentiation 
in OC. bakeri to the phenomena of senescence is so strong as to 
suggest a similar interpretation for both. 
The experiments will be continued. 
September 1, 1905. 
