566 



MEMOIRS OF THE INATIO^'AL ACADEMY OF SCIENCES. 



Plate TJI. 



Figs. 1.S8, ]S0. Parts of trausverse serial sections tbrouffb tbe embryo of Pala'monefe.i rulga^-is, at 

 the stage when pigment is just appearing in the eyes. In the anterior section (Fig. 

 188) the retiuogen is a unicellular layer. x305. 



Figs. 100-191. Parts of serial trausverse sections through the brain, the optic ganglia, and eye of 

 an embryo of Al2)heu.i heterochelifi. In the anterior section (Fig. 190) the clusters of 

 cells which represent the ommatidia are well shown. Numerous ganglion cells are 

 dividing. x305. 



Fig. 193. Part of transverse section through eye, optic ganglion, and brain at a later stage, x 305. 



RKFERBNCE LETTERS. 



A. }, first .antomia. 



.41)., abdomen. 



cc, cryst.alliiie cone cells. 



itnh., intercepting; menilirane. 



mes., mesoderm. 



Itet., retina. 



rtl.', rndimeutary eighth proxim.al retinnlar cell. 



sog., brain. 



T., telson. 



A'., stratum of large ganglion oells. 



1, li, 4, proxim.al, exteriKil middlr, .and distal segments of optic ganglion. 



