350 GERMINAL ORGANIZATION INDUCTION PHENOMENA 4 



{grosso tnodo dorsal, middle, ventral parts) and testing the effect of these antisera 

 on the cultivation of different marginal territories of the gastrula (Inoue and 

 Ishikawa, 1956). They generally yield structures corresponding to a degradation 

 of a more ventral type. This result fits in well with the idea that the pieces used as 

 antigens were already on the way toward building up the specialized components 

 of notochord, myotoms, pronephros, lateral plate and hematoblasts. When 

 cultivated in the presence of the corresponding antibodies, they were prevented from 

 building up the proteins corresponding to their presumptive level, but remained 

 able to form the proteins appropriate to the more ventral organ. This seems to 

 show that the more dorsal parts of the middle layer have a larger repertoire of 

 hierarchizedsyntheses than the ventral parts, and that the richness of this repertoire 

 corresponds to a high, middle or low morphogenetic potential. 



[f) Modifying intrinsic morphochoresis by operative and biochemical means 



The results of the preceeding biochemical measurements and of serological tech- 

 niques are, indeed, purely descriptive. Their meaning will be made clearer by the 

 consideration of some other experiments able to influence greatly later events of 

 morphochoresis. 



Analysis would clear the striking correspondence between vertebrates and 

 echinoderms. Concerning the latter {cf. Riinnstrom, 1928, 1954), all possible 

 combinations between blastomeres occupying the various tiers along the main 

 axis have been explored (Horstadius, 1935, 1950). The well-known hypothesis 

 of the two opposite and interwoven gradients has been carefully tested. No doubt 

 there are two "scales" of animalizing and vegetalizing tendencies, and that by 

 juxtaposition of different levels, a new equilibrum can be attained. A reciprocal 

 influence of cells of various origin is certain, and thus, for simplicity, we can 

 speak of induction. In this case, it appears to be a pvirely experimental process, 

 not active in the whole morula, or only as a conservative device. Its effective 

 mechanism is not known. At first view, a transfer of some agent seems probable. At 

 closer inspection, a regrouping of the "tendencies" towards both poles would also 

 be plausible; this could mean either transfer, or simply inhibition in the inter- 

 mediate zone. On the other hand, attention has been repeatedly drawn to the 

 immediate rearrangement of the combined cells. If we think of the production of 

 a- and [3-granules (p. 332) and similar events, the new shape acquired by the cells, 

 their respective conditions of respiration and other interactions could well be 

 important. However, in spite of these suggestions, it seems difficult to escape the 

 possibility of a transfer of some active agents. 



Another group of results concerns the effects of various chemicals on the same 

 two tendencies. The two classical agents are the vegetalizing LiCl and the 

 animalizing NaCNS. Not only are they able, if adequately used, to counterbalance 

 each other, but their action can be combined with well-planned operations in the 

 most amazing way. 



In vertebrates, we may recall first the action of these two chemical agents. 

 The fundamental difference in organization is so deep, however, that it would 

 not be reasonable to search for a close correspondence with the two preceding 

 effects. LiCl acts on both the cephalo-caudal and the dorso-ventral hierarchy 



