2^ Discoveries of Muller and others in the 



circular eminences, terminating internally in points which 

 are embedded in the dark-coloured pigment, and there at- 

 tached to the extremities of the white tuft-like filaments of 

 the optic nerve. These transparent cones have, however, 

 only their internal and more slender 

 extremities inserted in the dark violet- 

 coloured pigment, their upper and larger 

 end extending above and out of the 



*— T(nnflDI)/inrfn/nni^(fff W^^ ^^ coloured matter. Fig. 46. re- 

 ^fy[lfllry/V^"/x.i presents a section of the eye of the 

 Monoculus apus, as seen under the microscope. a, the 

 uncovered and rounded ends of the crystalline l3odies, their 

 apices being concealed in the dark pigment ; b, the white tuft- 

 like filaments of the optic nerve, which are attached to the 

 apices of the crystalline bodies. 



The cornea is without any trace of facets, and is thrown 

 oflp and reproduced with the skin. A similar structure of the 

 eye probably exists in all the Monoculi and inferior Crus- 

 tacea. In the Daphniae, the crystalline bodies are pear-shaped, 

 very short, and few in number ; their smaller extremities only 

 are inserted in the dark pigment. The cornea is without 

 facets. The same kind of organisation is observed in the 

 genus Limnadia of Brongniart ; and, according to Dalman's 

 representation, the surface of the eyes of Trilobites is similar 

 to what is seen in the Monoculus apus. In the Gammarus 

 Pulex there is this difference, that the eye is immovable. 



Fig. 47. represents a 

 48 section of the whole 



P eye of the Gdm- 



Q S^ marus Pdlex. Fig. 

 48. represents some 

 of the crystalline bo- 

 dies detached. 

 The eyes of the Cyamus Ceti, or whale louse, appear at 

 first sight to be simple, on account of their extraordinary 

 minuteness ; but, under the microscope, there can be seen an 

 aggregation of semicircular and transparent crystalline bodies 

 lying beneath a smooth cornea, and projecting through a 

 stratum of dark pigment. The eye, however, is so small as 

 to prevent any accurate examination of its several parts being- 

 made. 



From this statement it becomes tolerably certain that the 

 crystalline bodies, sometimes conical, at others pyriform, are 

 organs corresponding to those commonly found in the com- 

 pound eyes of the other Crustacea and of insects, with this 

 difference, that here the cornea has no facets, and that 



0C75 



