480 GERMINAL ORGANIZATION INDUCTION PHENOMENA 4 



Each phase is intensely constructive, first in the synthesis and storage of the 

 materials and energetic resources, secondly in the production of devices necessary 

 to morphogenesis, and finally in the mutual interplay of such devices in the succes- 

 sive steps of induction. Similarly, all organelles present in the nucleus or in the 

 cytoplasm are in constant activity, and if the most conspicuous changes take place 

 in the cytoplasm, it does not mean that the nucleus is passive. On the other hand, 

 if disturbances in the nucleus are less easily compensated for than those of the 

 cytoplasm, it does not mean that genes necessarily have the leading role through- 

 out development, as specialized geneticists would be too tempted to assert. Al- 

 though nuclear factors are probably active in the successive phases of ontogenesis, 

 as is suggested by experiments with hybridization {c.f. Baltzer, 1950), by trans- 

 plantations of nuclei (King and Briggs, 1954) and by the existence of many 

 mutations which interfere with different processes at various stages {cf. Gliicksohn- 

 Waelsch, 1954; Griineberg, 1948, 1950, 1957; Smith, 1956, etc), it would be exag- 

 gerated to consider genes as the operating staff. Of course, their role for the selec- 

 tive adoption of the specific or individual characters cannot be questioned. How- 

 ever, during gametogenesis and the morphogenetic phase of development, control 

 of genes seems less essential than the general functions of the nucleus (Dalcq, 1956b, 

 1957b). These functions are accomplished through continuous interaction with 

 cytoplasmic components which are an integral part of the endowment inherited 

 from the parent organisms, especially from the female. The cytoplasm of the egg 

 comes from the one of the primary gonocytes of the female gonads, and it is now 

 fairly well established that the yolk originates from general metabolic processes 

 which are hormonally controlled. Thus, the link between the successive genera- 

 tions is both nuclear and cytoplasmic, and even related to sex hormones, a relation 

 which is quite plausible. The differentiation of the chromosomes into multiple 

 loci is balanced, or nearly so, by the numerous metabolites and enzymes inter- 

 mingled in the cytoplasm. Both are an integral part of the basic material of heredity. 



The tasks of development are accomplished by the utilization of biochemical 

 systems and by organelles which are fundamentally the same as those existing 

 in the adult cells. However, there are special ontogenetic mechanisms which deserve 

 attention. In gametogenesis, we observe growth of cytoplasm typical to each 

 species, since it is free of any additions other than yolk, which is even sometimes 

 lacking; the nucleus performs functions and acquires a composition which is 

 never observed at other phases. After fertilization and during the mitotic phase of 

 morphochoresis, the cytonuclear interplay is probably maximal, and the cyclic 

 elaboration of the a- and ^- granules systems at least accompanies the establish- 

 ment of the morphogenetic pattern, which is mainly cortical. This intriguing 

 activity seems one of the most specifically embryonic ones. Thereafter, the striking 

 process of kinematic morphogenesis introduces the mechanisms of induction, 

 which are of gradually increasing complexity. Induction regulates morphochoresis 

 and controls most, and perhaps all of the differentiations. 



Investigators have succeeded in disclosing some substances which have appre- 

 ciably extended our biochemical understanding of the processes involved in the 

 highly complex transformations from gamete to yovmg embryo. These key-substances 

 are the nucleic acids and their proteic compounds, the mucopolysaccharides and 



