19i PKOFESSOR E. EAY LAXKESTER AXD A. G. BOURNE. 



as they do in the lateral eye ; and occasionally we find proe- 

 nuclear in place of post-nuclear phaospheres. No phaospheres 

 occur in the nerve-end cells of Androctonus. 



The peculiar shape of the ommateum (as shown in a right 

 and left vertical section at right angles to the animal's long 

 axis) is exhibited in the figure and also the peculiar bending of 

 the rhabdoms. The drawing is diagrammatic in so far as that 

 only one plane of nerve-end cells is drawn, whilst the rhabdoms 

 are represented as uncut. They, of course, really lie each in the 

 axis of a group of five cells, of which some are omitted from 

 the drawing for the sake of clearness. Very perfectly pre- 

 served and well-stained sections, similar to the drawing, were 

 obtained by the use of nitric acid, followed by borax carmine 

 (after washing). The inter-retinular pigment cells were, how- 

 ever, not preserved. 



Pigment in the Optic Cells of the Central Eyes. 



We find it difficult to decide as to whether pigment granules 

 are ever to be found actually within the nerve-end cells of the. 

 central eyes of Scorpions. Analogy with the nerve-end cells of 

 the lateral eyes would render it highly probable that the nerve- 

 end cells in both cases are pigmentiferous, the pigment being 

 limited to a superficial layer of the cell. At the same time very 

 thin sections, such as that drawn in fig. 9, seem to show that in 

 the special instance of the central eye the pigment granules are 

 not really in the protoplasm of the nerve-end cells, but always in 

 fine branches and processes of interstitial cells. The question is 

 one which must be left undecided for the present. It is, however, 

 important to notice (what will be further described below) that 

 in Limulus the nerve-end cells of the central eye certainly con- 

 tain pigment granules within their own proper substance. 



Comparison or the Lateral and Central Eyes of Scorpions 

 WITH those of other Arthropods hitherto described. 



In his great work Grenadier has described the so-called 

 " unicorneal " eyes of several Spiders, the " unicorneal " eyes 

 of Insect larvae and adult Insects, and the *'multicorueal " eyes 



