BY THE PRESIDENT. 
109 
briefly examine this. We know that light can be deprived of its 
ultra-violet rays if allowed to pass through a solution of sulphate 
of quinine, and that the luminosity of the beam is not sensibly 
weakened by its transmission. Now, Sir John Lubbock* has told 
us that out of 480 daphnias placed in a trough of water, 354 sought 
that portion illuminated with ordinary light, and only 126 re¬ 
mained where the incident rays had been deprived of those that 
were ultra-violet. The same naturalist has shown that ants remove 
their pupae from the ultra-violet rays of the spectrum, and prefer 
to be under glasses of other colours than violet. Yet when sulphate 
of quinine was placed over violet glass, the ants accepted the shelter 
as well as that of the glasses of the other colours with which he 
experimented. Ants with their eyes blinded with varnish are not 
affected by ultra-violet rays. It would therefore seem that the 
ultra-violet rays are visible to the daphnias and ants, although they 
are not so to us. This leads us to think that while we are groping 
in darkness, other animals may in a greater or less degree see their 
way, just as, when quiet appears to us to reign in our study, to a 
spider the room may resound with the stridulations of its future 
mate. The expression that cats see in the dark, i.e. in places which 
are dark to us, is not so absurd as it may appear. 
The sense of sight may be said to be possessed by an animal 
which is enabled to perceive, by means of a special organ, different 
values of light, but the exact anatomical representation for such a 
degree of vision is not known. Nor can we, without the most 
careful experiments, learn from the observations of the habits of the 
lower animals that they possess organs with such limited functions. 
The difficulty is realized in watching the eyeless hydra travelling 
towards the place where the direct rays of the sun are penetrating 
the water. The same phenomenon occurs with plants. Again, 
when we examine the so-called eyes of other members of the Coelen- 
terata and of the Yermes, we do not know whether the visual 
sensation exceeds that of mere light, as opposed to form and colour. 
It is, on the other hand, comparatively easy to form an opinion 
as to the possession of sight by the vertebrate whose habits are 
more related to our own, if only from observation we can ascertain, 
for instance, whether in its locomotion it avoids obstacles. But 
there is even a more trustworthy and extended source of infor¬ 
mation. We know the minute anatomy of our own visual organs, 
and when we find similar structures in other animals we know 
their function but not the extent of the function. We find differ- 
* ‘Journal Linnean Soc.,’ Zoology, vol. xvi, p. 127. See also ‘The Senses 
of Animals,’ and ‘ Ants, Bees, and Wasps.’ 
