86 



The Mechanism of EvoiiUTioN iir Leptinotaesa 



architecture. I distinguish two major types of agents : basal agents, which in 

 all experiences are properties of the whole type and do not segregate in any of 

 the normal reactions incident to development or in crossing, thus retaining their 

 integrity; and definite agents, or those that are specifically concerned in the 

 determination of the specific aspect that some quality presents. Of the basal 

 agents there are clearly two groups, those that I have called the basal factors, 

 few in number, and always properties of the whole, never altered or inter- 

 changed, and which may be the possible mixture of groimd-substance colloids 

 that seems to be the basis of the cell organization, and chromatic receptors, the 

 material substratum upon which the great majority of the determining agents 

 seem to find their distinctive seat of localization in the gamete. Of the definitive 



Table 2. 



agents there are two groups — a small one, always, associated with the basal 

 factors and having a distinct action as determiners of action, the cytoplasmic 

 determiners ; and the chromatic determiners, which are by far the most numer- 

 ous and the agents that commonly interchange in crossing. Of these four 

 classes I am of the opinion that the basal factors and the cytoplasmic deter- 

 miners are located in the colloidal matrix of the gamete and the chromatic 

 receptors and determiners in the nucleus. 



Of the basal factors I have found nine such cases of activity, each concerned 

 with certain general types of activity in the organisms, and with which specific 

 determiners act to produce any given result. I have no evidence of their segre- 

 gation or fragmentation, nor any evidence of their having been modified in any 

 experimental operations to which I have subjected my materials. The combina- 

 tion of these nine basal factors constitutes the phyletic base — ^that which in the 

 constitution has been likened to a nucleus, and in a certain sense it is a nucleus 

 of potential activities, needing only the special definitive agent go give expres- 

 sion to some concrete manifestation in the organism. 



