300 The Senses of the Lower Animals. [July, 
But here is a creature darting rapidly about, and yet able 
to turn and wind between a number of small obstacles. If 
this is touch, seated in the wings, in the lobes of the ears, 
or in the leaf-like appendages which in some species adorn 
the end of the nose, it is so highly subtilised as almost to 
deserve the rank of a distinct and independent sense, fulfil- 
ling, as it does, functions for which the ordinary feeling or 
touch of man and other animals is as impotent as it would 
be for recognising a colour or a sound. 
The possibility of other senses than the five with which 
we are endowed will at once appear if we reflect that of all 
the so-called “ physical forces ” light is the only one of 
which we have a direCt perception. We only recognise heat 
and electricity when they give rise to some phenomenon 
which appeals to our sight and our feeling. Now, it is plain 
that senses may exist which take direCt cognizance of the 
eleCtric or thermic state of bodies. Had we such senses 
they would evidently enable us at a glance to distinguish 
bodies which, without formal scientific examination, appear 
to us identical, and to recognise changes of condition which 
now escape us. An animal possessed of a magnetic sense 
would, for instance, be able, without any mental effort, to 
direCt its course northwards or southwards, and in crossing 
an unknown region would enjoy all the advantages which 
we derive from the use of the compass. 
The possibility of new, undiscovered senses is of course 
greatest in the Invertebrates, and chiefly in the Articulates. 
We find these creatures executing actions which from our 
point of view demand reason of a higher grade than we are 
willing to concede to beings so widely different from our- 
selves, and — what is much more to the purpose — in which 
we fail to trace in other points such effects as we might 
naturally expeCt to flow from the possession of a highly- 
developed intelligence. There appears in their economy a 
mixture of wisdom and folly more incongruous than we at 
least can imagine may be detected by higher beings in our 
own. When, further, we examine their structure, we find 
organs of sensation upon whose functions we are far from 
being able to pronounce with full certainty. 
Concerning the organs of sight in inseCts there can for- 
tunately be no dispute, but their eyes differ so widely in 
structure from those of the vertebrate animals as to offer 
not a few unsolved problems. 
Many groups possess two distinct kinds of eyes — the 
larger or compound, and the smaller, simple, or so-called 
ocelli. The former — found in all mature inseCts, save cer- 
