DISCUSSION 215 



as contrasted with the single one in the other two animals, 

 may be of systematic importance, but it is doubtful whether 

 it is of appreciable functional value to the subgenus. 



The significance of many of the subgeneric variations in 

 other particulars of the soft parts has been discussed under 

 the proper headings. Most of such differences are slight 

 or else compHcated; but the chief ones, lending themselves 

 readily to tabulation, may be summarized as shown in 

 table 4. 



Of the nine items above which have to do most intimately 

 with the aUmentary tract, it is seen that in the four (in- 

 cluding the Uver but excluding other glands) which concern 

 particulars located craniad to the small intestine, the 

 development may be said to be least in Homodontomys and 

 most in Teonoma, with Neotoma occupying an intermediate 

 position. The remaining items are not uniform in this 

 respect, but the average of development is least in Neotoma 

 and most in Teonoma, with Homodontomys occupying the 

 the intermediate position. These facts are difficult of 

 proper interpretation, in regard to Neotoma especially. 

 The remaining details in this table have already been 

 discussed. 



The differences found among the three subgenera of wood 

 rats are too numerous to admit of a detailed summary, nor 

 is a summary and lengthy discussion of conclusions desirable 

 in the present instance, for as previously explained, the 

 present work is meant to constitute a basis to expedite 

 other contributions now in progress concerning highly 

 speciaHzed mammals. 



As might be expected, none of the differences herein 

 mentioned may be termed startling, but many are of definite 

 importance, and most of them are of considerable significance 

 in one way or another. Clearly there are two trends in- 

 dicated. In one the development would seem to be purely, 

 or at least largely, phylogenetic, with Neotoma occupying 



