44 Trans. Acad. Sci. of St. Louis. 



Peres Cecropias. The solid lines indicate the number of 

 males emerging on the given day, and the dotted lines 

 the females. 



In one or two cases, especially the Polyphemus, the 

 rate of emergence was so uniform or so scattered that 

 this graphic method tells us less than does the simple 

 mean. But in most cases the two lines run generally par- 

 allel, with only the space of a day or so between them. 

 In fact, the nicety with which so nearly every increase 

 or decrease in the frequencies of the males is followed 

 by a corresponding change in the females is quite sur- 

 prising. The female curve follows the male curve like 

 its shadow. For instance in the South St. Louis Cecro- 

 pias, fig. 6, one could almost estimate from a glance at 

 the curves that the males appear on an average between 

 1 and 2 days before the females (the calculated mean is 

 really 1.84 days). 



Since the males have this precedence in 7 of the 8 lots 

 of material here considered, we feel that it must be more 

 than mere coincidence. The Polyphemus (figs. 2-4) show 

 this difference less than do the other species ; in one lot, 

 the Massachusetts Polyphemus (fig. 3) the females show 

 a decided priority, and in the other two lots the priority 

 of the males is not so great as in the other species. 



But throughout the series of curves we see unexplained 

 vacillations in the emergence of the whole population, 

 especially in the cases where the lines for both sexes sud- 

 denly drop low or to in the midst of the season (as on 

 May 22 in fig. 4, and May 10 in fig. 8), or where the 

 whole population goes up or down together. Here an- 

 other factor becomes apparent. We add to the list of 

 figures a curve (the broken line, fig. 9) showing the mean 

 temperature for each day, along with the emergence of 

 all insects on that day, all species combined. This ex- 

 plains at a glance a great deal of the fluctuation of the 

 emergence of the entire population, although we cannot 

 see that it exerts a particularly greater influence upon 

 one sex than upon the other. In a large number of cases 



