296 EARLY DETERMINATION IN DEVELOPMENT 



originate from materials other than the normal material. The 

 paper by Holtf reter ( 1944 ) , showing that action of several chemi- 

 cal and physical agents bring about the same results, supports the 

 interpretation of the liberation of evocating substances from ab- 

 normal materials. 



Fig. 6. Petromyzon larvae, head reconstruction: A, control; B, Li+- 

 treated larva; a habenular ganglia; b, first branchial pouch; c, notochord; e, 

 epiphysis; f, pharynx; 1, otocyst; m, midbrain; n, olfactory organ; p, plica 

 rhombo-mesencephalica; pr, forebrain; r, hindbrain; x, protuberance of 

 chiasma; Vi, first trigeminal ganglion; V,, second trigeminal ganglion; VII, 

 facialis; IX, glossopharyngeus; X, vagus. (From Ranzi and JaneseUi, 1941.) 



The Petromyzon embryos seem to react to Li+ and SCN" just 

 as the amphibians. LiCl-treated embryos are described by Ranzi 

 and JaneseUi (1941) (Fig. 6). NaSCN-treated embryos showed 

 large notochord and hind-brain enlargements ( Ranzi, 1945 ) . This 

 field is open to further research. 



The lithium chloride-treated embryos of an ascidian {Ciona 



