166 



THE EYE IN EVOLUTION 



Lobster 



We shall see ^ that the stalked eyes of such Decapods as the lobster, the 

 shrimp and the prawn are remarkable in that the nervous connections run to the 

 procephalic lobes of the cerebral ganglion up the long stalks containing the optic 

 lobe with its series of ganglia and intervening plexiform zones. The presence 

 of a three-layered compound retina and a ganglionated optic lobe makes these 

 crustacean eyes the most complex among Invertebrates (Figs. 147, 693). 



The eyes of Crustaceans living at ocean depths are rarely so well formed as 

 those inhabiting littoral or shallow waters ; as a rule — to which, however, there 

 are marked exceptions, particularly in the more active forms — the number of 

 ommatidia in bathypelagic forms is decreased and the pigment is scanty or 

 absent so that the organ functions as a superposition eye ^ adapted for dim 

 illumination (Edwards and Bouvier, 1892). 



THE COMPOUND EYES OF INSECTS 



The compound eye of Insects has excited interest and admiration 

 for centuries (Figs. 149 and 150)^; indeed, the faceted cornea attracted 

 the attention of the pioneer Dutch microscopist, van Leeuwenhoek, 



li r 



Fig. 149. — The Eyes of Insects. Fig. 150. — The Compound Eye of 



An old anatomical drawing from Swammer- ^ 



dam (Byhel der Natuure, Leyden, 1737). Section through the compound eye. 



Although inaccurate in details, the surface showing the optic lobe consisting of 3 



of the intact compound eye is seen on the left, optic ganglia, and the protocerebrum 



a partially dissected eye on the right, as well as (below) (Norman Ashton). 



the 3 central ocelli (reproduced by permission of 

 the Cambridge University Library ; by courtesy 

 of Dr. Pirenne and the Pilot Press). 



' p. 521. 2 p_ 169^ 



' For the descriptive anatomy of the compound eyes of insects, see Miiller (1826), 

 Gram ;iier (1879), Exner (1891), Hesse (1901-8), Seaton (1903), Dietrich (1909), Johnas 

 (1911;, Bedau (1911), Geyer (1912), Demoll (1912-17), Zimmermann (1913), Jorschke 

 (1914), "Bugnion and Popoff (1914), Priesner (1916). Ast (1920), Cajal and Sanchez 



