294 



EARLY DETERMINATION IN DEVELOPMENT 



Olf.. 



Fig. 4. Cross sections of amphibian tadpoles: A, control tadpole; B, 

 NaSCN-treated tadpole. Dorsal view of brain and sense organs reconstruc- 

 tion: Ai, normal tadpole; B,, NaSCN-treated tadpole; Co, notochord; Cr, 

 lens; Di, diencephalon; E, epiphysis; Ga, ganglion; G.c, notochord sheath; 

 L.O., optic lobes; Mi, myelencephalon; Oc, optic cup: Olf., olfactory pit; 

 Ot., otocyst; P., first cross section passing through the pronephros; Te., 

 telencephalon. Short dotted line indicates ependymal cavities. Long dotted 

 line indicates notochord. (From Ranzi, 1954.) 



