176 Transactions of the Boyal Society of South Africa. 
conditions. As an experiment, a few dark specimens were kept in a white 
enamelled trough open at the top, but after a fortnight there was no 
appreciable colour change : on covering them with a sheet of white paper 
the toads turned yellow within twenty-four hours. This obviously sug- 
gests that the afferent impulses of the reflex are visual, the eyes being 
situated on the top of the head. 
