Periodicity, S)C. upon the Development of Trisects. 65 



(lerance in number of the sexes was reversed ; in the one-year 

 brood it was as 59'46 per cent. $ to 40*54 $ ; and in the two- 

 year brood as 34-375 per cent, $ to &5'Q'Z5 $ . This fact is 

 easily to be explained by the above-mentioned fact of the earlier 

 development of the males of the one-year brood ; the females 

 coming out the latest, there is a greater chance for them than for 

 tlie males to become a two-year brood. 



1 have also to note another remarkable fact upon this two- 

 year brood, viz., the numerical proportion of this brood in alter- 

 nate years. Thus, the even years, 1844-46-48-50, produced 

 ninety-three of one-year brood and thirty-seven of two-year 

 brood; but the uneven years, 1845-47-49-51, produced eighty- 

 nine of one-year brood and only three of two-year brood. The 

 number of my observations is certainly too small to state this fact 

 positively, but it seems to me sufficiently marked for calling 

 attention to this fact. 



The differences in advancing or retarding the time of coming 

 out in the month of June and the first days of July are certainly 

 occasioned by differences of temperature, principally in the month 

 of May. In the first warm days in the month of May the pupae 

 receive an impulsion by which the proper formation of the perfect 

 insect in the pupa case is set in action. Those which resist this 

 impulsion remain to the following year; thus the periodicity of 

 the species prevails over the influence of the temperature. 



Further experiments are in accordance with this view. The 

 pupa state in insects is best adapted for physiological experiments 

 on the transformation of matter in animals. They live and em- 

 ploy matter like other animals, but take no additional food. 

 Their food is deposited in their bodies in the adipose tissue, 

 accumulated during the larva state. The larva eats not only for 

 itself, but also for the future pupa, which is not able to take food 

 from without. Hence it is not necessary to take into account the 

 food consumed by the animal (as would be required in experiments 

 with the larva), whereby such experiments are much facilitated. 

 I tiierefore commenced by making a series of calculations of the 

 weights of the pupa^ at different times. The loss can thus only 

 represent the loss by respiration, and the amount of the loss will 

 represent the activity of the vital functions. I cannot detail in 

 exlenso all the points connected with the researches which I have 

 made, and will, therefore, only give some of the results. First, 

 the mean loss sustained by the insects from April to the time of 

 their appearance in the perfect state, calculated for the early 

 period in series of ten days' duration, and subsequently from day 



VOL. I. THIRD SERIES, PART II. MAY, 1862. F 



