266 THE POPULAR SCIENCE MONTHLY. 



These he is always ready to assist and encourage to the extent of 

 his ability. As will be seen from the foregoing sketch, he is an 

 indefatigable worker, and, to the brief notices of his articles 

 given above, space will only allow a few other references to the 

 discoveries he has made and the theories he has advanced in the 

 various lines of zoological and geological research. 



When Agassiz came to this country, he brought with him not 

 only an interest in zoological subjects, but, as well, that enthu- 

 siasm which made his name famous in connection with the study 

 of glaciers. He j)ointed out the existence of local glaciers in the 

 White Mountains, but Dr. Packard traced out further than ever 

 before the extent of this local system, following these rivers of 

 ice from Mount Washington and the adjacent peaks down the 

 valleys of western Maine. This work on glaciers was still fur- 

 ther elaborated in his large memoir on Labrador, mentioned 

 above, and led to other speculations of a zoological rather than 

 of a purely geological character. 



These were that the existing insect fauna of at least the North- 

 eastern United States had its origin from a circumpolar Tertiary 

 fauna. The facts for this conclusion were in part the following : 

 Oswald Heer and Dr. Asa Gray had conclusively shown that the 

 plants of the same region had thus originated, the Tertiary rocks 

 of Greenland containing many genera which are characteristic 

 of the American flora of to-day. Now, as is well known, there 

 is the most intimate connection between the distribution of many 

 insects and the plants on which they feed, and the habitats of 

 many insects can only be accounted for upon some such suppo- 

 sition. For these in detail the student should seek Dr. Packard's 

 " Monograph of the Geometrid Moths," but we can mention one 

 instance. Certain butterflies and moths are known to-day only 

 from the colder regions. They are found in Labrador and far- 

 ther north, while in the United States they only occur in the 

 widely separated mountain-regions of New Hampshire and Colo- 

 rado. These, it is assumed, must have lived near the edge of the 

 great continental ice-sheet of glacial times, and must have oc- 

 curred in all the intervening extent of country. As the ice re- 

 treated and the territory became warmer, the plants on which 

 the larvse fed could only find conditions favorable to their exist- 

 ence on these high mountain-regions or the isothermal but lower 

 lands of Labrador. This view of the origin of the fauna of the 

 United States has since been adopted by many writers, and re- 

 ceives its most complete exposition in Dr. A. R. Wallace's " Geo- 

 graphical Distribution of Animals," but without credit to Dr. 

 Packard, who advanced it several years before. 



In morphological work, the studies on the development of the 

 sting of the bee must be mentioned. Dr. Packard pointed out 



