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EARLY DETERMINATION IN DEVELOPMENT 



(1954): vegetalized embryos show a smaller ciliar tuft at the 

 animal pole than the controls; these embryos develop into larvae 

 in which the ectoderm is reduced whereas the entoderm is hyper- 

 developed and in certain instances it protrudes ( exogastrulae ) . 

 The animalized embryos develop with a very large ciliar tuft; in 

 these embryos entoderm and mesenchyme are reduced. 



Vertebrate cyclopic embryos, obtained by Stockard (1907) in 

 Fundulus and by Cotronei ( 1922 ) in amphibians through the ac- 

 tion of MgCl2 and LiCl, may be considered as originated from 

 the same causes which induce vegetalized larvae in sea urchins. 

 Adelmann (1934) and Lehmann (1937) showed that LiCl in- 

 duces an inhibition of prechordal plate and of the notochord in 



Fig. 2. Animalized sea urchin embryos. (From Lindahl, 1936; Tamini, 

 1941; Backstrom, 1953.) 



amphibians (Fig. 3). Therefore the cyclopy originates from a 

 disturbance in the induction process, and the hypodevelopment 

 of the notochord and of the prechordal plate corresponds to the 

 sea urchin vegetalization. Later Backstrom ( 1953 ) showed a re- 

 duction in organ development and in the animal half of the 

 Xenopus embryo ( therefore small embryo ) . So far we are unable 

 to state whether this phenomenon can be observed in other am- 

 phibians. 



An increase of notochord in the amphibians is induced by 

 NaSCN (Ranzi et al, 1946) (Fig. 4). Statistical research carried 

 out by Corti at Milan on Rana esculenta embryos in the tailbud 

 stage showed the following average number of notochordal cell 



