§1] 



UPON THE KATE OF GROWTH 



43a 



were the same. At the end of one month* three tadpoles 

 were taken at random from each vessel and measured. In the 

 following tables are given the average length and breadth of 

 these tadpoles (from series of 1876 and 1877), and also the 

 lengths compared with that in 'white light : — 



TABLE XLII 



Average Dimensions of Tadpoles eeaeed behind Clear and Colored 

 Screens ddring One Month 



Similarly, averaging the dimensions of the tadpoles at the 

 expiration of two months, we obtain : — 



TABLE XLII a 



Average Dimensions of Tadpoles reared behind Clear and Colored 

 Screens during Two Months 



Tadpoles reared in the dark were uniformly slightly larger 

 than those reared in red light, while violet and blue light show 

 themselves especially favorable to the growth of the frog. 



* During the first days of development in the cases of the frog, the snail Pla- 

 norbis, and the sea-urohin Echinus, there is, according to Driesch ('91), no 

 difference in the rate of growth behind various colored glasses. The diverse 

 effects of different rays appear only in later stages. 

 2f 



