S. RANZI 



297 



intestinalis) may develop into exogastrulae (Ranzi and Ferreri, 

 1945) (Fig. 7). In some of these larvae the notochordal cells do 

 not differentiate. In some other larvae notochordal cells may ap- 

 pear with little difference from entodermal cells. It is concluded, 

 therefore, that there is an entodermization of notochordal cells 

 induced by LiCl. NaSCN-treated embryos show a larger neural 

 plate. In Ascidia malaca embryos, treated with LiCl, Nieuwkoop 



Fig. 7. Exogastrula from Li + -treated embryo of Ciona: ec, ectoderm; 

 en, entoderm; mi, myoblasts. 



(1953) found only exogastrulae of the second type.* I did not 

 have the opportunity to study the material further, because I 

 deemed it suflBcient to find certain malformations in ascidians 

 corresponding to those of vertebrates. 



* Nieuwkoop (1953) interprets the organization of exogastrulae without 

 notochord by admitting that intrinsic differentiation tendencies, extrinsic 

 realization factors, and tissue affinities are required for embryonic differ- 

 entiation, and that realization factors are blocked by LiCl. Perhaps Nieuw- 

 koop's realization factors represent the demoUtion of preexisting protein 

 structures inhibited by L1C1, as discussed below. 



