1 58 MYSIS— CORYC.EUS— COPILTA. 



In illustration of the compound eyes of Crustacea, I 

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



In the higher Crustacea 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 (iV^ N'^^, iV^^\ 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 retinulso comparatively short ; while 

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

 short, and the retinulae long. 



The eye of Corycseus (Fig. 107) is very interesting. 

 It is extremely large in proportion to the size of the 



Fig. 107.— Corycjeus (after Leuckart). a. b, The eye. 



animal, extending from the front of the head to the 

 beginning of the abdomen. The perceptive part of 

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

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

 single element of a compound eye. 



The eye of Copilia is also very remarkable, the 

 retinula 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 



