INSECT METAMORPHOSIS. 34! 



for each specimen. Pupation as well as emergence of moths was 

 checked every day between 6 and 6:15 o'clock in the evening. 

 The chrysalids were weighed immediately afterwards, so that 

 the age of the weighed pupai ranged from o to 24 hours. The 

 data obtained were biometrically studied according to the 

 commonly used formula?. On account of the remarkable sexual 

 dimorphism the data were collected for either sex separately. 

 The total number of pupae was 818, of which 234 male and 188 

 female were thyroid fed specimens and 171 male and 225 female 

 control animals. Emergence occurred from 782 chrysalids, viz. 

 218, 182, 161 and 221 specimens respectively (cf. the number of 

 animals in separate experiments in Tables I. and II). 



The first chrysalis of the whole material appeared on June 

 24th. The average terms of pupation of the thyroid-fed and 

 of the control caterpillars calculated in relation to the above 

 term of the "first chrysalis" are recorded in Table I. We 

 notice that the observable differences of the terms of control and 

 experimental material were positive only in 3 cases, in the 

 remaining 5 being on the contrary negative. The difference was 

 here biometrically significant exclusively in the males of the 

 second experiment, the ratio of the difference to its probable 

 error in this case only approximating the required number 4. 

 Moreover, on surveying the data referring to the duration of 

 the pupal period (Table II.) we observe that here too the differ- 

 ence between the control and the thyroid-fed animals is not 

 always positive, the ratio of the difference to their probable 

 errors oscillating only between 0.05 and 2.5 and therefore being 

 in no case significant. This indicates that neither the rate of 

 the hystolytical processes in the caterpillars nor the rate of 

 development in the chrysalids were in our experiments influenced 

 by the thyroid added to the food. In other words, this substance 

 did not elicit any changes in the course of metamorphosis of the 

 examined insects. 



From the theoretical point of view this result requires however 

 the following remarks. It has often been emphasized that the 

 influence of glands of internal secretion may be not only of 

 various intensity, but even essentially different in relation to 

 the developmental or growth stage of the animals experimented 



