LATERAL AND CENTRAL EYES OF SCORPIO AND LTMULUS. 191 



The INTRUSIVE PIGMENTARY CONNECTIVE TISSUE is a very 

 important element in the building up of the retinal body, 

 which has been on the one hand misinterpreted by Von 

 Graber, and on the other hand overlooked by Grenadier, whose 

 observations upon the central eye of Scorpions were under- 

 taken with a view to the controlling of Von Graber's results. 



No intrusive connective tissue (except in the form of blood- 

 vessels) is described by Grenacher in other monomeniscous 

 eyes (such as those of Spiders) similar to the central eyes of 

 Scorpions. It would, perhaps, be worth while searching for it 

 in those eyes. The structures which we consider as intrusive 

 connective tissue in the central eyes of the Scorpion may be 

 compared to the interneural cells of the lateral eyes. Like these 

 they are pigmentiferous and serve to fill up the spaces between 

 the several nerve-end cells, and between these and the ommateal 

 capsule. But whilst we regard the interneural cells as ecto- 

 dermal in origin, that is, as belonging to the same germinal 

 layer as the cells of the hypodermis and the great nerve-end 

 cells, we find reasons for considering the intracapsular pigmentary 

 tissue of the central eyes of Scorpions as derived from meso- 

 blast and of the nature of connective tissue. 



We have not embryological evidence for this conclusion, and 

 depend entirely upon the branching, inosculating character of 

 the pigmentary cells, and upon the analogy of the pigment- 

 cells surrounding the retinulae of the polymeniscous eyes of 

 Insects and Crustacea, which are very generally held to be of 

 the nature of connective tissue, as also upon that of the 

 "packing-tissue'* to be described below in the central eye of 

 Limulus. 



We are by no means anxious to maintain that the more 

 epithelium-like cells amongst what we are about to describe 

 as " intrusive intracapsular connective tissue'* may not be of 

 distinct origin from other portions of this pigmentiferous frame- 

 work, and referable to interneural cells of ectodermal nature, but 

 any such distinctions must be based upon embryological facts, 

 which we do not possess. In the present state of knowledge 

 it seems most convenient and justifiable to hold that in the 



