ON THE OKIGIN OF VERTEBRATES. 



261 



Crustacea ; they are usually known by the name of liver 

 diverticula, but as they take no part in digestion, but, on the 



le 



Fig. 11. — The brain, eyes, and anterior termination of tlie alimentary canal of 

 Artemia, viewed from the dorsal aspect, Br., brain; I.e., lateral eyes; 

 C.C., median eyes ; Al., alimentary canal. 



contrary, represent that part of the gut which is most active in 

 absorption, the term liver is not appropriate, and it is therefore 



A B 



Fig. 12. — A, the formation of the retina of the eye of Ammoccetes (after Scott) ; 

 B, the formation of the retina of the eye of Ammoccetes, on my theory. 

 B., retina ; I., lens ; O.n., optic nerve fibres ; Al., cephalic end of inverte- 

 brate alimentary canal; V., cavity of ventricles of brain; AJ.d., anterior 

 diverticulum of alimentary canal ; op.d., optic diverticulum. 



l)etter to call them simply the pair of anterior diverticula. 

 Our knowledge of their function in Daphnia is given in an 



