180 THEIR CHANGES OF COLOUR. 



chanced to direct his attention to them. For some 

 time, he was dehghted with observing the changes 

 of colour, described by him in the following words, 

 in his most deservedly popular work, " First Steps 

 to Botany." " At first," the flies, after bursting 

 from their chrysalid state, " are greyish white, 

 with a waxy transparency ; in a few seconds they 

 became bluish, in a few more like the mainspring 

 of a watch, and after some minutes, gi-eat part 

 of them is grown quite black." * He soon, how- 

 ever, noticed, that after resting a little while on the 

 walls of the apartment, they began to bestir them- 

 selves, and gained in time an open window, from 

 which the back-yard of the dweUing-house was seen, 

 surrounded on every side by high walls and build- 

 ings. The moment this position was attained, rest 

 was at an end. They opened their wings and flew 

 into the yard, not to rest upon its walls, but to hold 

 their course right into the air, above the houses 

 which hernmed them in, and thence scatter in every 

 direction fi'om the height they had attained. Of 

 hundreds which were evolved from the pupte cases, 

 not one rested in the yard, but, from the window, 

 darted right into the air, and held its unwavering 

 flight upwards. Perhaps, under such circumstances, 

 the wind might exercise a considerable influence on 



Second ed. p. 149. 



