37." 



THE AMERICAN NATURALIST 



[Vol. L 



or less spherical world converge either way we go. Furthermore, 

 if we place confidence in oceanic bridges which have been washed 

 away, piers and all, the lines of dispersal are apt to be fre- 

 quently discontinuous. 



7. Location of Least Dependence upon a Restricted Habitat.— 

 For example, certain plants and animals which, in the region of 

 New York City, are found only in sphagnum bogs, such as those 

 of the Jersey pine barrens, occur more widely distributed 

 farther north. According to this criterion their center of dis- 

 persal would be in the north and this may be true. Again, liz- 

 ards occur, in the region of New York City, only or chiefly in 

 these same pine barrens, while farther south they run about 

 wherever they can get sunshine. According to this criterion the 

 ancient center of dispersal of lizards was somewhere near the 

 equator, but this may not be true. 



8. Continuity and Directness of Individual Variations or 

 Mm/ijici/xjns Radiating from tin Center of Origin along the 

 Highways of Dispersal. — This criterion is probably stated rather 

 more fully than was meant. If we knew all this, the problem 

 would be solved. Perhaps Adams meant that continuity and di- 

 rectness of modifications (•" individual variations" gets us into 

 the biometric-mutation discussion and that is another story) 

 point out the highways of dispersal from the point of origin. 

 His reference on the next page to Osborn's law of adaptive 

 radiation indicates that this is the proper interpretation of this 

 criterion and, if so, the present author has no quarrel with it 

 except to point out once more that we are left in doubt as to 

 which way to follow the lines. 



9. Direction indicate d In/ Biogi ographieal A ffinities. — I am 

 not certain as to what this means. I suppose a given group 

 which is neotropical at the present time has biogeographical affin- 

 ities with other present-day neotropical groups. If we know 

 the centers of dispersal of the other groups we have a working 

 hypothesis concerning the eenter of dispersal of the group in 

 question. If this be what is meant, it seems to be probable. 



10. Direction indicated by the Annual Migration Routes, in 

 Birds.— This criterion is meant to apply only to birds and I fear 

 we know too little concerning the intricate problems of bird mi- 

 gration to say whether their present-day routes of annual mi- 

 gration follow the route of ancestral dispersal or not. Probably 

 they do not, as the birds would be expected to change their 

 routes with changing environmental conditions. Furthermore, 

 although it is believed that birds return to their ancestral home 



