16 



Bulletin Wisconsin Natural History Society. [Vol. 8, No. 1. 



to hatch at 11 p. m., September 1st, as in Lot No. 6 and after the first 

 9V, hours 137 (or 87%) of them had hatched; the remaining 21 eggs 

 (13%) hatched during the next 9% hours, making a period of hatching 

 of 19 hours. 9 times the period of deposition. The curve of distribution 

 is a normal freqtiency curve skewed. (Fig. 7.) 



The following discussion is to be taken for what it is worth, 

 which is no more than the actual value of the data. A large 

 part of it is unwarranted if based on the data alone. However, 

 it may be useful. Attention is directed to the fact that but a 

 single species is referred to. 



What has actually happened? First, in each separate lot of 

 eggs, we find an inherent 2 variation in the duration of embryonic 



h i in x 



Figure 7. — 158 observations. 



The curve is similar to that of 

 Lot No. VI. 



'h 



Fig-ure 8. — 6S3 observations. 



Frequency of hatching in the lots 

 combined/ expressed roughly 

 in percentages. The added line 

 is the curve of temperature in 

 centigrade degrees. 



development causing a variable period of hatching; hatching 

 occurs in such a manner as to become distributed over a curve 

 of frequency having one or two modes. Secondly, periods of 

 deposit short in regard to time, are apparently unrelated to the 

 duration of the period of hatching. Thirdly, the duration of 

 the period of hatching — and similarly, the duration o the period 

 of deposit — is measurable, not by its frequency distribution which 

 has to do with relations, but by that time which is a mean of the 

 times of its beginning and ending ; and the duration of the period 

 of embryonic development is to be taken as the period of time 

 included between the mean times of the period of deposit and the 

 period of hatching. 



2 Apparently inherent ; the lots were all in the same environment for the 

 same period of time, the first lot not being separated from the last by more 

 than 6 hours, during which there were no abnormal fluctuations in tempera- 

 ture. 



