EYELIDS 95 



eyelids which must have arisen independently 

 in those families. Where there is a continuous 

 perforated membrane, as in some Clupeidse 

 (e.g., Dussumieria, Fig. 8), the condition pre- 

 sented calls to mind that of the Oegopsid cuttle- 

 fishes, where the outer covering of the eye is 

 likewise perforated. No doubt the two condi- 

 tions are physiologically comparable. 



FIG. 8. Eye of Dussumieria showing perforated adipose eyelid. 

 The outline of the pupil is seen below the transparent [dotted] 

 adipose membrane. 



Raptorial or prehensile appendages amongst 

 invertebrate animals offer further analogies. 

 Chelate extremities occur alike in Crustacea 

 and Arachnida ; and the characteristic clasp 

 knife appendages of the Stomatopod Crustacea 

 (Squilla) are found again in Orthopterous insects 

 (Mantodea) and in Neuropterous insects (Mantis- 

 pidse). In Chiromantis, a tropical African genus 

 of frogs allied to Rhacophorus, the two inner 

 fingers of the hand are opposite and opposable 

 to the two outer fingers, so that its structure re- 

 sembles that of the grasping hand of chameleons. 1 

 All these cases belong to the great category 

 of opposable extremities, some of which are 



1 G. A. Boulenger, Catal. Batr. Sal, 1882, p. 92, pi. x., Figs. I 

 and 2. 



