158 MYSIS — CORYC^US— COPILIA. 



In illu:tration of the compound eyes of Cru-tacea, I 

 give a figure of an eye of Mysis (Fig. 106). 



In the higher Crustaoea the nervous elements of 

 the eye are, moreover, very complex. There are no 

 less than four optic ganglia (Fig. 106), and there is 

 a chiasma, or decussation of fibres {N\ N^\ N^^\ iV'""), 

 between each. 



The eyes of lobsters and of crabs offer a curious 

 difference. In the former, the crystalline cones are 

 very long, and the retinulse comparatively short ; while 

 in the crabs, on the contraiy, the crystalline cone is 

 sbort, and the retinulse long. 



The eye of Corycaeus (Fjg. 107) is very interesting. 

 It is extremely large in proportion to the size of the 



Fig. 107.— Coryc^eus (after Leuckart). a, b, The eye. 



animal, extemling from the front of the head to the 

 beginning of the abdomen. The perceptive part of 

 the eye (i) is, therefore, far removed from the lens (a). 

 The eye of Corycaeus appears to represent, in fact, a 

 single element of a compound eye. 



The eye of Copilia is also very remarkable, the 

 retiuula being, at about the end of the first third of its 

 length, bent at a right angle. Here also the eye is 

 about one-third as long as the body. 



The ocelli of Crustacea have not been much studied 

 with reference to their microscopic structure. Those 



