42 DISCOPHORiE. Part III. 



profile [Fif/. 15 Ir) or from above or below {Fif/. 7 1^). In profile it would seem 

 to be similar to that of the lobe (/" f) until we come to the end [Fig. 8 h^ Jf' h'), 

 where it suddenly thickens to more than double its extent, as seen toward the 

 base ; but in the view from above it shows a sudden increase in thickness {Fig. 7 h^), 

 which it retains especially at the base, but toward the end decreases in a measure, 

 aud then at the end thickens again as in the profile view {Fig. 8). The cells 

 of the outer and inner wall below the eye are very similar among themselves, 

 but vary somewhat according to their situation; and in the eye itself {h) the 

 variation is very strongly marked. The cells of the outer wall (/i^), as well as 

 those of the lobe (y®), may be comjaared to broad polygonal prisms, disposed side 

 by side in a single layer; their contents are homogeneovis and transparent, nor 

 does there appear to be any mesoblast. At the base {Figs. 7, 8, and 15 A*') of 

 the eye they decrease in length with greater or less ra^iidity according to the 

 degree of expansion or contraction of the peduncle. Sometimes the decrease is 

 rather gradual {Fig. 15 h), and they may be easily traced as cells all over the 

 end of the eye-facets {h) ; at other times, and this is the most frequent case, they 

 suddenly decrea.se in length and assume the form of thin polyhedral disks {Fig. 8 h), 

 thus constituting a tenuous layer {Fig. 8 h, Fig. 14 h^) all over the end of the organ 

 of vision. The cells of the inner wall {Figs. 7, 8, and 15 /r) are also prismatic 

 in shape, aud vary in length according to the degree of expansion of the peduncle, 

 and appear different according to the position in which the latter is viewed, whether 

 from above or below or in jn-ofile : in the latter aspect {Figs. 8 and 15 J^) they 

 resemble those of the outer wall very closely; but in a view from below {Fig. 7 h^) 

 they have a more prismatic columnar look, and vary in length from double to 

 thrice their breadth. Whether in one view or the other, they rapidly increase 

 in length after they enter the faceted eye ; and here the}^ lose their prismatic shaj^e, 

 and take on a polyhedral conical form {Fig. 8 A* li/) and converge nearly to one 

 point {h'). At the base {h^) of the facets their conical form is not so apparent; 

 but at a short distance beyond this they are strictly conical, and all have their 

 apex at the centre {h') of the sphere. And now, too, another element enters into 

 the com^iosition of these cells: as we view them from the outside, and endwise 

 {Figs. 7, 14, 15 A*), they aj^pear much darker and more highly refractive, as if 

 they were filled with some oily substance ; but when we obtain a jjrofile and 

 sectional view {Fig. 8 h* K), we find that the highly refractive body (/i*) occuj)ies 

 about one quarter of the outer end of each cell; and all these standing side by 

 side in one layer, each in its respective cell, produce the effect of a third wall {h^). 

 A closer examination of these bodies reveals the interesting fact that they are 

 lenticular (PI. XP. Fig. 16 (5 i), and have the form of a plano-convex lens; the convex 

 face (x) is turned toward the outer end of the cell, and the plane face toward 



