SENSE ORGANS. i 
wave-length and the sensation so imparted we call sighz. 
Lower vibrations than this we call heat, and we have, pro- 
bably, sense-organs for the discernment of heat. Vibrations 
of a still lower grade (from 40,000 to 30 per second) we per- 
ceive by our ears and the sensation we term sound. Lastly, 
the actual contact of particles upon a specially sensitive 
surface gives us the closely allied senses of smell and taste. 
Sight involves the perception of light or shade and also, 
as a higher faculty, the discernment of actual images. 
The former alone exists in a number of low animals and 
the latter is only added when the organ of sight has the 
addition of an optical apparatus, known as the dioptric 
mechanism. It is highly probable that many animals 
have organs for the perception of vibrations higher or 
lower than those of sight and the “sense” thus produced 
is quite inconceivable to us. It may differ from our senses 
as widely as sight from hearing. 
In the case of hearing much the same remarks hold. 
There is little question that many aquatic animals have 
organs of equilibrium or of motion which render them 
cognisant of low mechanical vibrations of water produced 
by the approach or proximity of a foreign object. In 
certain land-animals (e¢g., Bats) there appears to be much 
the same kind of faculty, which enables their possessors to 
avoid objects without the aid of eye, ear or nose. 
We may therefore divide sense-organs into three arbitrary 
groups, as follows :— 
1. High-vibration organs.— ' Roark 
(1) Possible organs for perception of vibrations above 
A760 wave-length. 
(2) Eyes for as ae of vibration A760 to A390 wave- 
(3) Possible ene for vibrations of lower frequency. 
2. Low-vibration organs.— ar A. 
(1) ‘ Auditory” organs for perception of vibrations above 
40,000 per second. 
(2) Auditory organs for perception of vibrations 40,000 to 
30 per second. j 
(3) Motion-organs for perception of vibrations 30 per 
second to a single vibration. 
3. Contact-organs — a : 
(1) Olfactory organs for finely divided particles. 
(2) Taste-organs for food. 
(3) Touch-organs for mechanical contact. 
M. 3 
