352 ANNUAL OF SCIENTIFIC DISCOVERY. 



multiplicity of individuals. The male is about one third larger than 

 the female. The drumming apparatus of the male, Dr. Burnett had 

 made the subject of careful microscopic study. He had found it to be 

 integumental in its nature, not presenting any relation, either by 

 structure or analogy, to the respiratory system. It is situated on each 

 side, between the thorax and abdomen, the head of the drum being 

 just under the attachment of the wings to the body, and of the size of 

 a marrowfat pea. It consists of a tense, dry, crisp membrane, crossed 

 by cords or bars, produced by a thickening of the membrane, which 

 meet on one side at the point of attachment of the muscles, which, by 

 their contraction, keep it stretched. The sound is produced by a series 

 of rapid undulations, running from the contracting muscles across the 

 drum. The upper part of the abdomen seems to act as a sort of sound- 

 ing-board ; when a portion is removed the sound is sensibly diminished. 

 A dry condition seems to be necessary to the perfect action of the 

 drum, as, on wet days, or when it is moistened, the sound is very much 

 diminished. The drumming sound is heard four or five hours during 

 the day, principally between the hours of twelve and two. In the 

 female there is no drum, nor any trace of the muscular apparatus be- 

 longing to it. As an illustration of the immense numbers in which 

 these insects appear, Dr. Burnett stated that he saw an oak tree, on 

 every leaf of which were six or eight individuals. 



ON THE ECONOMY OF SEVENTEEN YEAR LOCUSTS. 



THE following is an abstract of a paper read before the American 

 Association, Albany, by Dr. W. I. Burnett, of Boston : 



A careful analysis of the conditions of animal existence has led some 

 to believe in the special creation of the separate faunas in the locali- 

 ties in which they are found. Prof. Agassiz has traced the various 

 phases under which this question may be considered, and in it may be 

 found reasons for the particular creation of such fauna and its immu- 

 tability through any period of time. A question allied to this, but 

 based upon a different, and, perhaps, more enlarged view of life, is the 

 one of the primitive numbers of each species. In this we call to our 

 aid embryology and its allied branches, but the influences which civil- 

 ization has wrought, both directly and indirectly, upon the ratio of 

 mortality of animal life, affect much the validity of our conclusions. 

 Nevertheless, the general tenor of all such inquiries is to show that the 

 number of each species must have been pretty near that which we find 

 in its natural and undisturbed state, instead of a single pair, as other- 

 wise viewed. In a locality the natural relations of which to animal 

 life have not been disturbed by the agencies of man, we have a right 

 to infer that the existing state of destructive elements of life is a fair 

 expression of the past, and also that the present rate of the mortality 

 of a species is that to which it has been subjected during past times. 

 If, in a term of human experience of one hundred or a thousand years, 

 the natural prolicity of any well known species only keeps pace with 

 its relative mortality, so that the number of that species, at the end of 

 that time, is about the same, it is very difficult to comprehend how, 



