EYES OF CRUSTACEANS 



IO7 



fluviatilis, the shrimp, Crangon, and the prawn, Palcemon, exhibit an extra- 

 ordinary complexity and diversity of structure, and they afford a most 

 valuable insight into the relation of the sensory receptive cells to those of 

 the ganglia in the central nervous system. The early stages of develop- 

 ment of Astacus were first studied by Reichenbach (Fig. 74), who showed 

 that the superficial cells which will give rise to the future eye are at first 

 indistinguishable from those of the cerebral lobe and appear to be con- 

 tinuous with them. Further, it is believed by Kappers and others that 

 the cells of the cerebral lobes have been derived from the superficial 



Fig. 68. 



-Lepidurns Kirkii : semi-diagrammatic, sagittal section showing the median 

 eye and its relation to the supra-oesophageal ganglion or brain ; also the 

 relation of the oesophageal connectives to the gullet and of the heart and genital 

 gland (r. ovary) to the alimentary canal. 



(Redrawn from Parker and Haswell's Textbook of Zoology.) 



