careful study of past experience of nearly a century ; by weighing 

 all the other conditions, he had ascribed certain eastern limits 

 beyond which the Rocky Mountain Locust could not perpetuate 

 itself or do continued damage, and he regretted to find Dr. Engel- 

 mann, on what he must believe were insufficient grounds, lending 

 the weight of his authority to the opposing statement that there 

 is not sufficient evidence for the opinion. If he were to announce 

 that he had discovered the CEneis simidea in the Mississippi 

 Valley, or in Missouri, every well-informed entomologist would 

 at once declare it a mistake, and say he had confounded it with 

 some other butterfly, because the CEneis is known to be confined 

 to the alpine regions of Labrador and the White and Rocky 

 Mountains, and is absent from all the intermediate country. The 

 classified knowledge we have on the subject establishes certain 

 limits outside of which the species does not thrive, and there is 

 every reason to believe cannot, except by man's assistance ; and 

 the same may be said of a whole lot of alpine and sub-alpine 

 plants. The same is true of many insects and other animals. — 

 Past experience shows that the Rocky Mountain Locust cannot 

 change its habits. It is indigenous to the sub-alpine heights of 

 the Northwest, and its individual life is bounded by the spring 

 and autumn frosts. Species are sometimes found to be limited 

 in a wonderful way to certain areas, and it cannot be explained 

 why some can and others cannot adapt themselves to different 

 conditions. The genuine Colorado Potato-beetle spread eastward 

 through man's agency, as the intermediate territory was settled. 

 The bogus Colorado Potato-beetle, however, did not and does 

 not spread in the same manner, as it cannot subsist on the culti- 

 vated potato. — As to the objection to the expression "prescribe," 

 the word has various synonyms, one of which is "establish," and 

 few would fail to see that it was used in this last sense. 



Dr. Engelmann then said, as his name had been mentioned in 

 the discussion, he would offer a few remarks. The Potato-beetle 

 and its allied Doryphora would furnish examples to sustain his 

 views. One has shown its ability, within the past fifteen or twenty 

 years, to spread itself over a wide range of country, while the 

 other, its congener, had remained confined in its original area. 

 Twenty years ago the Potato-beetle was as little known as its 

 congener. It did not feed on potatoes until the potato had been 



