342 



WILLIAM PATTEN. 



granules, aiul forms au unpaired mass of cells below and a 

 little in front of the eyes proper; it is supplied by the paired 



Fig. 9. — Diagrammatic views of Arthropod and Vertebrate embryos, to 

 illustrate the stages in the infolding of the brain, optic ganglia, and eyes ; 

 the heavy black lines indicate the ganglionic pits, and the shaded por- 

 tions the parts that are infolded. — A. Acilius. B, C, and Z). Three 

 stages in the development of Scorpio. E. Limulus. F. Hypothetical 

 transitional form. G. Vertebrate, au. Ear. e^. Eye on third segment 

 of fore-brain of Limulus. g.v^-^. Ganglionic invaginations, /.e. Lateral 

 eye. /./. Lateral furrow, m. e. Median eye. np. Neuropore. o. pl^-^. 

 Optic plate, s. s. o'-''. Segmental sense-organs of thorax, x '^iid s. s. o*. 

 Very large ear-like sense-organ. 



colourless nerves^ n'. Toward the late larval stages the white 

 mass becomes constricted off as a solid diverticulum of the 

 primitive bulb, and finally lies some distance from the surface 

 as a cylindrical mass of cells filled with white pigment ; in all 

 stages the walls of the cells composing this body develop 



