Chap. II. AURELIA FLAVIDULA. 43 



the base (C) of the cell; the edge is abrupt and as if cut awa}^, so that it has 

 a polyhedral contour, with generally six sides (PI. XP. Figs. 11 and 16 <3 i), and 

 each side fits exactly against the several sides of the cell {8 i]). In consequence 

 of the arrangement of the lenses in a spherical contour, these sides are not par- 

 allel to the axis of the lens, but converge slightly from the anterior convex face 

 backwards, so that in a view from behind {F!g. 11) there appears to be a double 

 outline (i). The anterior convex face (k) does not touch the outer end (()') of 

 the cell, but there is a very shallow space (t) between the two. The posterior 

 plane face is perforated by a comparatively broad ajjcrture {Figs. 11 and 10 v) 

 leading into a cylindrical cavity (^), which occupies the axis of tire lens, and 

 penetrates a little more than two thirds of its thickness in a direct line toward 

 the anterior face, and terminates abruptly. The sides of the cavity are convergent 

 backward, and trend parallel to those of the lens, and the transverse diameter is 

 a little more than one quarter of the breadth of the lens. When seen from the 

 posterior face {Fig. 11), this cavity appears to be divided into as many compartments 

 {a) as there are sides to the lens ; but we find that these compartments, or 

 diverticuli, are superficial {Fig. 16 u), and proceed from the posterior end of the 

 cavity, near its aperture {Fig. 16 v), close beneath the flat face of the lens, to 

 the sides (<? i), and strike them perpendicularly half way between the angles. 

 The outlines of this cavity are rather irregular, especially in the diverticuli {p,), 

 and, being more or less wavy, they produce the effect of a wall, in profile. It 

 is this cavity which has the appearance of being a mesoblast, in the centre of 

 each cell, when they are looked at endwise {Fig. 7 h^). If the eye is cut to 

 pieces, the lenses drojo out, and may then be turned in every direction for the 

 study of their shape. In this manner we have been enabled to turn a lens up 

 on one of its sides, and trace the actual curvature of the anterior face {Fig. 16 x) ; 

 and we found this curvature to be spherical. Here, then, we have all the elements 

 of an optical apparatus, sufficient to produce a distinct image. No one will pretend 

 to deny that the eye of an insect is a true eye, having all the properties of 

 distinct vision; and if so, we are fully justified in claiming for the eye of Aurelia 

 the same faculty. Curiously enough, too, the relations of the different parts of 

 this apparatus are the same as among higher animals; but whether the several 

 parts perform similar functions we will not pretend to affirm. First, we have the 

 cell of the outer wall {Fig. 16 a), with its outer face for the cornea and its 

 contents for the anterior chamber of the aqueous humor; then the posterior wall 

 (/3) of the same cell («) and the anterior wall {8) of the cell (»y) containing the 

 lens, combined, would be the membrana pupillaris, which is imjjerforate ; next, the 

 space (k) between the membrana puiDillaris and the front of the lens Avould be 

 the posterior chamber of the aqueous humor; then comes the crystalline lens {& i); 



