n 



188 PEOFESSOE E. EAT LANKESTER AND A. G. BOURNE. 



sac" (Schlauch). Grenacher, on the other hand, denies the 

 existence of Von Graber's anterior and middle nuclei; for him 

 the nerve-end cell is a single cell of elongated form, with one 

 large nucleus — that which Von Graber calls nucleus of the 

 ganglion cell. Our conclusion as to the nerve-end cells of the 

 lateral eyes of Euscorpius and Androctonus entirely agree with 

 those of Grenacher as to these structures in general. Grena- 

 cher has not examined, it must be remembered, the lateral eyes 

 of Scorpions. In describing the nerve-end cells of the central 

 eyes of Scorpions we shall have occasion to point out the 

 existence of structures adjacent to the nerve-end cells, which 

 have probably led Von Graber to hold the erroneous views as 

 to the nerve-end cell which he has advanced. These structures 

 have escaped the notice of Grenacher. 



Central Eye of Androctonus funestus. 



The central eyes of the Scorpions are considerably larger 

 (from twice to three times linear) than the lateral eyes. As in 

 the lateral eye, we distinguish lens and ommateum. The lens 

 is a simple laminated mass of cuticle, which we must dismiss 

 on the present occasion without attempting any examination of 

 its optical properties. It would, no doubt, be important to 

 compare these with those of the lateral eye, &c. 



The ommateum of the central eyes differs essentially from 

 that of the lateral eyes, in the fact that it is not composed of 

 one layer of cells, but consists of two layers of cells, one super- 

 imposed upon the other, and separated from it by a strong 

 laminated membrane (PL X, fig. 8n; PI. XI, fig. 11 w). 



The anterior layer (o in the figures) is known in other simi- 

 larly constructed eyes as the *' Glaskorper,'^ or 'Witreous 

 body," whilst the hinder layer may be called the " retina," or 

 " retinal body." As will be seen when we examine the retinal 

 body more fully, it does not consist of a simple layer of nerve- 

 end cells, but is complicated by the presence of a large bulk of 

 nerve-fibres within the eye-capsule, and by the presence of 

 what is of more importance morphologically, viz. intrusive 

 connective tissue. 



