CRABS AND SHRIMPS 199 



universally present as the compound eyes. On the fore- 

 head of the Honey-bee they are well seen, as three black 

 shining globules, placed, as in the Dragon-fly, in a tri- 

 angle. 



CHAPTER XI 



CRABS AND SHRIMPS 



IT is always interesting to trace the varied forms and 

 conditions under which any particular function is per- 

 formed; and particularly to mark, in creatures very 

 remote from us in the scale of being, the organs devoted 

 to the senses which are so requisite to our own comfort. 

 We have already seen some of these diversities, in exam- 

 ples taken from the classes Mollusca and Insects; and will 

 now examine some more, as they appear in the Crustacea. 

 If you look at the head of a Crab, a Lobster, or a 

 Prawn, you will see that it is furnished with jointed an- 

 tennae, like that of Insects ; but whereas in insects there is 

 never more than a single pair, in the creatures of which I 

 am speaking there are two pairs. In the Prawn you may 

 suppose, at first sight, that there are four pairs; but that 

 is because the internal antennae terminate each in three 

 many- join ted bristles, in structure and appearance exactly 

 like the bristles of the outer pair, two of the three being 

 nearly as long as the outer, while the third is short. In 

 the Lobster, the internal are two-bristled, both bristles 

 rather short, while the external are very long. In the 

 Flat-crabs each pair is simple, the inner minute, the outer 

 long. In the great Eatable Crab each pair is very small, 

 and they are dissimilar. 



