28 JOURNAL OF THE KOYAL IIOETICULTURAL SOCIETY. 
the dark- coloured one was quite blind. Prof. Henslow quoted an analogous 
case in which the eyes of shrimps had been covered, and the result was 
that these shrimps were not coloured like the normal ones, in imitation of 
their surroundings. Prof. Henslow then observed that there appear to • 
be two distinct kinds of mimicry : (1) automatic and unconscious ; 
(2) brought about by conscious action of the creatures. As an example of 
the first he cited colour, mentioning the green-leaf insects and several of j^- 
tbe caterpillars shown on the screen by Mr. Blake. The same kind of 
similarity applies to all desert animals, as may be seen in a case in the 
entrance hall of the South Kensington Museum. A remarkable illustra- 
tion of this kind of mimicry has lately been described of domestic mice, 
which have become established on sandhills in Dublin Bay. Though 
14 per cent, are still of the usual dusky slate, the great majority are of 
the colour of the sandhills, though transitional colouring exists among 
these mice. That light is not the sole cause would seem probable from 
the fact that many animals change from brown to white when the 
temperature is lowered ; thus the stoat becomes the " ermine " in winter. 
Good examples may now be seen of this change in Russian hares — grey- 
white and buff- white — now being offered for sale in the shops. 
In the case of the shrimps and the plaice described above they had not 
assumed a light colour, because, being blind, light reflected from the 
sand had not afiected the pigment cells of the skin by acting automatically 
through the optic nerves of the eyes ; while in the normal shrimps and 
plaice these had become adapted in their colouring most probably by that 
means. 
As instances of conscious action, he alluded to the attitudes of cater- 
pillars when alarmed, as described by Mr. Blake ; and the habits of certain 
crabs which fix bits of sea-weed all over their carapaces, and of the 
" stick " insect which never arranges its legs symmetrically but irregularly 
so as to resemble more accurately a twig lying on the ground. 
Prof. Henslow then alluded to the fact that mimicry in nature is of 
a very wide extent ; for it not only applies in all probability to most 
families of animals, but to the vegetable kingdom as well. Thus, e.g., 
the fleshy stems of Cacti, Euphorbias, and Stapelias are almost exactly ahke, 
because they grow under similar conditions, and this case is sufficient to 
illustrate the general law, that the same or at least very similar external 
forms and colours &c. arise when the beings live under very similar 
conditions, since all protoplasm — the living basis of life — has the power 
to respond to external impulses and to build up similar structures. When, 
however, we try to investigate the immediate causes, and how they work, 
we appear to be baffled at almost every point. He thanked Mr. Blake 
very heartily, for, without any doubt, such subjects, handled in the way 
this had been, set people thinking, and to be made to think was always 
of the greatest possible service to every one of us. 
