STRUCTURE OF EYE 



157 



or stalk-eyed) they are situated on more or less 

 elongated pedestals. In some of the lower forms, 

 tbough less complex, they are very large, occupyins', 

 as in the curious Leptodora (Fig. 105) of our deep 

 lakes, the whole fiont of the head ; while in Corycseus 



Fig. 106.— Eye of Mysis (after Grenadier), n. Nuclei; Lf, facets; Kk, cryBtalline 

 cone.s; n', cells of the retinula; Rl^ retinula; Rm, rhabdom; Cp, blood-vessels; 

 N, fibres of the optic nerve ; N', iV", N''^, JV'^'\ decussations of the fibres of the 

 optic nerve; (?, G', G^', (?'", ganglia; M, muscles for the movement of the 

 eye-stalk; Km\ Km^\ nuclei. 



(Fig. 107) they extend to more than one-half of the 

 whole lenofth of tlie body. 



The higher Crustacea possess no ocelli. In the 

 lower species, on the contrary, a central ocellus is often 

 present, especially in the young state. 



