148 ACQUIRED CHARACTERS SEC. 



differently coloured surroundings on the common frog (Eana 

 temporaria) : Three frogs approximately similar in colour 

 were placed in three glass vessels, of which the first stood 

 on a black, the second on -a green, and the third on a white 

 surface, being surrounded up to a height of some five centimetres 

 with the same colour. After about an hour and a half, the frog 

 a on the black surface was the darkest, b on the white the 

 lightest, while the frog c surrounded by green was inter- 

 mediate in colour between the two. Hereupon the frog a was 

 transferred to the glass on the white, frog I into the one on the 

 black surface. After three-quarters of an hour they were again 

 examined, and a, was the lightest, b the darkest. Then c and b 

 were interchanged, and in a quarter of an hour c was the 

 darkest, while b was intermediate in colour between c and a. 

 When, finally, b and a were interchanged, a change of colouring 

 appeared immediately ; b became light again, and a took the 

 intermediate tint between b and c. The change of colour seemed 

 to be due to the fact that when the colour became lighter, the 

 pigment distributed over the skin was collected in particular 

 places in small dark spots, and when it became darker, it was 

 spread out more uniformly over the whole surface of the body. 



When I repeated the same experiment with the same 

 frogs on the following day I only observed a slight change of 

 colour, although this was still noticeable. But one frog and 

 a toad (Bufo vulgaris), which I had left during the following 

 night in a quite dark vessel, had both become blackish brown 

 in the morning. After I had placed them in the light on a 

 light surface the frog immediately began to get lighter in 

 colour, and continued to change gradually, so that after half 

 an hour it was brownish yellow. In the toad the change of 

 colour occurred much more slowly : only after some time 

 could I see that it was distinctly lighter, and it was a whole 

 hour before it became light brown. 



Three other frogs changed colour in the course of about an 



