Recapitulatory and Karyogenetic Characters. 101 



series of geographic sub-species succeed each other down the 

 Pacific coast, the most northern form being largest and with 

 dark brown markings, while further south they become progressively 

 smaller and lighter in colour, i.e., with less brown and more gray. 

 These various sub-species are co-terminous with each other in 

 their distribution and they form a very close, practically continuous 

 series. The conclusion was reached that while such discontinuous 

 variations as the red colour phase are independent of environmental 

 or functional influence, the continuous type occupying distinct and 

 adjacent geographic areas, represents the results of the stress of 

 environment on the species in its dispersal, leading to the gradual 

 differentiation of local races or sub-species. 



Sumner (1918), in his studies of the deer mice, Peromyscus 

 maniculatus, has arrived at similar conclusions regarding the 

 occurrence of both mutations and gradual differentiations, and 

 their geographic relationships. This subject is one which requires 

 much further investigation, but it is at least possible that this 

 continuous type of geographic variety in its origin involves the neo- 

 Lamarckian factor. 



The neo-Lamarckian principle. 



Experiments have shown that impressed modifications may 

 affect the offspring for at least two generations, and to this extent 

 the neo-Lamarckian principle has already been justified. The 

 mechanism of transmission in such a case is apparently different 

 from that of a mutation or a Mendelian character in a cross. The 

 latter appears to be determined in the nuclei, and therefore 

 transmitted as a stable and permanent feature. The acquired 

 character is temporary, cytoplasmic in origin, and will not be 

 permanently retained unless re-impressed generation after generation 

 until the nuclei of the germ cells are ultimately altered in their 

 constitution. 



The fixation of such an organismal character may require a 

 longer or shorter number of generations. What determines the 

 number of generations required is quite unknown at the present 

 time, nor is the modus operandi understood. But we may assume 

 that in the process, altered metabolic products in the cytoplasm 

 ultimately produce a modification of a chromatin element which 

 is permanent in character. It may be expected that such a 

 transformation will occur much more rapidly in some cases than 

 others. 



