AMERICAN ZOOLOGISTS AND EVOLUTION. 



loi 



eggs are less in number and smaller in size.* Mr. Robert Ridgway f 

 calls attention to the geographical variation observed in Dendroeca. 



The same author,^ in a discussion of a paper by Salvin in the 

 " Transactions of the Zoological Society of London," on the relation- 

 ships between the birds of Guadeloupe and the mainland, refers to the 

 present genesis of species, and points to the increase in size of the bill 

 and feet, the shorter tail and wings and darker colors, as character- 

 izing them. 



Dr. E. C. Coues,* in his studies regarding geographical variation 

 in color among North American insectivorous mammals, says : " JVIy 

 studies up to the present go to show a very interesting parallelism 

 with the state of the case I have determined for other small mammals, 

 notably the mice and gophers, and which my friend Mr. Allen has 

 admirably brought out in his studies of the squirrels. In some cases 

 I find almost identical effects of climatic or other conditions upon 

 the shrews and the mice of particular localities, by which they both 

 acquire the same fades loci. Present indications are that the normal 

 variability of the shrews in size, shape, and color is not less than has 

 been determined to hold good in various other families of mammals." 

 In this memoir Dr. Coues has verified a curious fact, first pointed out 

 by Professor Baird, of the modifications of the premolar dentition 

 w^iich the "Western species collectively, as compared with the Eastern, 

 have undergone : " A striking peculiarity of all the "Western species, 

 no matter how diverse in other respects, is to have the 'third pre- 

 molar ' decidedly smaller than the ' fourth,' while in all the species 

 east of the Rocky Mountains (with one possible exception) the same 

 tooth is as large as, or larger than, the other. Of the fact there is no 

 question ; it may be observed in an instant, and is unmistakable. Its 

 significance is another thing. Some of the Western species are scarcely 

 distinguishable if at all from their respective Eastern analogues, except 

 by this character, and they all show it." 



Professor A. Hyatt || finds in sponges geographical variation in 

 color, referring to similar features in birds as recorded by Baird and 

 others. 



Professor David S. Jordan,"^ in a paper on the distribution of fresh- 

 water fishes, presents a concise series of joropositions which govern 

 these animals in the United States. They all point to the action and 

 importance of physical conditions as governing distribution. Space 

 will permit only the quoting of the last proposition, which is a sum- 

 ming up of his conclusions : " The distribution of fresh-water fishes 



* "Culletin of the Xuttall Ornithological Club," vol. i, p. T4. f Ibid., p. SI. 

 X Ibid., vol. ii, p. 58. 



* " Bulletin of the United States Geological Survey of the Territories," vol. iii, No. 3, 

 p. 635. 



II " llemoirs of the British Society of Natural History," vol. ii, part iv. 

 ^ "American Naturalist," vol. xi, p. 607. 



