416 Wandering Cells and Muscles from the Optic Cup Epithelium 
There arise from the epithelium of the optic cup under normal con- 
ditions such varied tissues as muscle, branched and anastomosing pig- 
mented wandering cells, simple layers of epithelial cells and the nerve 
cells of the retina. The origin of the first two from the epithelium 
must modify our idea of a rigid specificity of the outer germ layer. 
Mauer’s* discovery that in the frog smooth muscle develops from the 
ectoderm of the skin; the possibility, according to Kodis, that wander 
ing cells may come from the ectodermal cells of the tadpole’s tail, and 
the numerous observations on the origin of lymphocytes from the epithe- 
hum of the tonsil shake our faith in the rigid specificity of the outer 
germ layer. 
*Mauer: Die Epidermis und ihre Abkommlinge. Leipzig, 1895. 
°>Kodis: Epithel und Wanderzelle in der Haut des Froschlossenschwanzes. Archiv 
f. Anat. u. Phys. Phys. Abt., 1889. 
