1910] 



Giranlt, Periods of Embryonic Development. 



15 



them had hatched; then followed a lapse of 6 or 7 hours; by the pass- 

 ing of the next 10 hours, 145 (67.44%) more had hatched and hatching 

 (45 eggs or 20.93%) was completed during the next 12 hours. Here 

 the period of hatching extended to from 42 to 44 hours, at least 40 

 hours longer than the period of deposition. The distribution shown 

 in figure 5 lies between that of the previous lots and those to follow, 

 approaching the single mode. (Cf. figs. 4, 5 and 6.) 



Lot No. VI. Thirty-seven eggs similarly deposited during a period of 

 15 minutes (2:15 to 2:30 p. M.) did not begin to hatch until 11 P. M., 

 September 1st. 24 hours after those of the previous lots and then after 

 9% hours 32 (S6.48%) had hatched; the remaining (13.51%) hatched 

 after 4 hours more. Here hatching was continuous, there being no 

 lapse and the curve of distribution (Fig. 6) shows but one mode; 



'/t 



'h 



Figure 5. — 215 observations. 



Figure 6. 



I'/, 2. 



-37 observations. 



Here the tendency approximates 

 that of normal frequency. 



the period of hatching was but 13 y 2 hours long, yet the period of 

 development was about 24 hours longer than in the previous lots. 



Lot No. VII. Eight eggs deposited in rapid succession during a 

 period of 5 minutes (2:31 to 2:36 p. m.) hatched almost simultaneously 

 at about 5 a. m., September 2d. Here the curve of distribution is 

 almost straight up and down and the period of development averages 

 longer than in most previous lots. 



Lot No. VIII. Two eggs deposited during a period of 15 seconds 

 (2:37 to 2:37:15 p. m.) hatched at 10:30 a. m. and at 11 p. m., Sep- 

 tember 1st, hatching extending over a period of 12 y 2 hours. Here, 

 the curve is indicated as bimodal, but actually it would probably take 

 the form approximately of the curve of normal frequency, so-called. 

 The period of hatching greatly exceeds the period of deposition and 

 the period of development is shorter than in the preceding lot. 



Lot No. IX. One hundred and fifty-eight eggs deposited in rapid 

 succession during a period of 120 minutes (2:40 to 4:40 p. M.) began 



