486 PHYSIOLOGY. 



animals, and in reference to it we may possibly be allowed to surmise 

 that they do not possess the power of distinguishing tones ; but in oppo- 

 sition to this, it may be mentioned, that their females would not be able 

 to distinguish the luring tones of the males from any other sounds, and 

 consequently their possession of a means of indicating their presence 

 would not much serve them ; and also the signs of recognition among 

 the bees, to which we shall have occasion to return below, is opposed 

 to it. There are also other instances of a mode of communication among 

 insects, by means of peculiar sounds. 



278. 



The way in which insects see by means of their eyes will be best 

 explained by Joh. Muller's investigations *. With respect to simple 

 eyes, we know, partly from their structure and partly by the direct 

 observations of Reaumur t and Hooke, who closed these simple eyes, 

 and then never detected the creatures moving in the direction of these 

 eyes, and that they only then flew whither their compound eyes could 

 survey their path, that these vertical points are actually eyes. Joh. 

 jMiiller has made it probable, from the structure of these eyes, that 

 their refraction must be very great, in as far as each ray of light suffers 

 a fourfold refraction, the first of which is produced by the convex 

 cornea, the second by the anterior convex surface of the lens, the third 

 by the posterior convex surface of the lens, and the fourth, lastly, by 

 the convex surface of the glassy body itself. This disposition presumes 

 an indistinct distant sight, as the object is thereby too great to be dis- 

 tinctly seen, but a well defined and distinct short sight. And, indeed, 

 we find in all the Arthrozoa, which have merely simple eyes, for 

 instance, in the Arachnodea, the power of sight agreeing with this 

 view, for it is only closely that spiders can see accurately, at a distance 

 the object appears to vanish from them. If we apply this to the simple 

 eyes of insects we shall find in them, likewise, that the function of their 

 simple eyes is adapted for a distinct close sight, and particularly for small 

 objects, which are difficult for the large field of vision of the compound 

 eyes to survey. They hence appear to make most use of their simple 

 eyes in narrow spaces, and as these simple eyes, as well as compound 

 eyes, are almost exclusively found in those insects which feed upon the 



* Zur Vergleichenden Physiologic des Gesichtssinnes, p. 3.VJ, \c. 

 t M^moires pourservir a 1'His.t. dcs Insectes, toiu. v, part i, p. 3t>3. 



