182 PROFESSOR E. RAY LANKESTER AND A. G. BOURNE. 



It is convenient to speak of the region in which the lateral 

 eyes of the Scorpion develop as the " ocular area/' 



A section vertical to the chitinous surface of the shield^ and 

 parallel with the optical axis of the lens through one of the 

 lateral eyes of A. fu nest us, presents before the pigment is 

 removed the appearance shown in Plate X, fig. 1, after the 

 removal yf pigment, the appearance shown in fig. 2, 



In the first place we notice in this, as in other Arthropods' 

 eyes, that the lens is simply a local enlargement of the cuticle, 

 and that the layer of epidermic cells usually called " hypo- 

 dermis," which produces the general cuticle, and is observable 

 at the sides of the section (PI. X, fig. 2 c), is continued beneath 

 the enlarged boss of cuticle, which acts as lens, and is cor- 

 respondingly increased in dimensions. This enlarged portion 

 of the hypodermis is, in fact, the soft or living tissue of the 

 eye, and may be distinguished from the lens in front of it by a 

 special name. We propose to call it the " ommateum." The 

 ommateum and the lens together form the eye. 



When series of sections of the ommateum of a lateral eye of 

 Androct. funestus are carefully studied it is found that the 

 ommateum is a simple enlargement of the single layer of 

 cells forming the hypodermis. It consists of a single row 

 or stratum of cells, which present a distinction among 

 themselves into two kinds. The two kinds of cells in the omma- 

 teum of the Scorpion's lateral eye are — firstly, the retinal or 

 NERVE-EJSD CELLS (fig. 2, h), in which the nerve filaments of 

 the optic nerve terminate (fig. 2, 7n) ; and, secondly, indif- 

 ferent CELLS (fig. 2,y and g), which are narrow and columnar 

 in form, similar in every respect to the ordinary hypodermis 

 cells in the neighbourhood of the eye, and like these latter 

 pigmentiferous. 



Both nerve-end cells and indifferent cells of the lateral omma- 

 teum apparently belong to the epiblastic layer, and are shut 

 olF together with the layer of hypodermis cells from the sub- 

 jacent connective tissue by a well-marked " basement mem- 

 brane," which in the region of the ommateum may be called 

 the eye-capsule, or, better, the " ommateal capsule." 



