212 PROFESSOR E. RAY LANKBSTER AND A. G. BOURNE. 



Pliaospliere. — A brilliantly refriugent spherical body found in tlie nerve-end 

 cells of Euscorpius italicus, E.os, usually behind, but sometimes iu 

 front of the nucleus. 



Monomeniscous. — Of the chitinous cuticle in front of an ommateum when 

 it has the form of a single lens. 



Polymeniscous. — Of that condition of the chitinous cuticle in front of an 

 ommateum when it is segregated or broken up into many lenses, only 

 found, and then not always, when there is a retinular segregation of the 

 ommateum itself. 



Epistatic. — Of a monostichous ommateum when the anterior ends of its 

 nerve-end cells abut upon the cuticular lens. Only observed in the lateral 

 eyes of Scorpio and Limulus. 



Apostatic. — Of a monostichous ommateum when it forms a cup or tube-like 

 depression below the cuticular lens, the lens not entering the lumen of 

 the cup or tube. 



Autochromic. — Of an ommateum in which all the pigment is developed in 

 cells of ectodermal (hypodermis) origin, and into which no connective 

 tissue penetrates. 



Exochromic. — Of an ommateum in which some, if not all, the pigment is 

 developed in intrusive connective-tissue cells, which penetrate deeply be- 

 tween the proper ectodermal elements of the ommateum. 



Vitrella. — A group of cells of a vitreous body which has become segregated 

 in correspondence with the segregation of the retinal body and of the 

 lens. A lens-facet, a vitrella and a retinula surrounded by pigmentiferous 

 cells constitute a single " element " of the compound eye of Insectu 

 hexapoda and of Crustacea. 



