340 GERMINAL ORGANIZATION INDUCTION PHENOMENA 4 



genetic role, a conclusion well in accordance with the penetrating views of Lallier 

 (1957) who insists on the prevailing role of basic proteins, left untouched by our 

 stains. For mammalian eggs, the available data also speaks against a primary role of 

 the metachromatic granules in morphogenesis. They are precisely prevalent in the 

 part of the egg devoted to mainly trophic functions, especially to the relations 

 with the maternal tissues. In ascidians, the link with morphogenesis is somewhat 

 less loose, and the fate of cells seems to depend largely on the relative proportions 

 of hyaloplasm, mitochondria — the role of which is emphasized by Reverberi (1956, 

 a, b; 1957a, b) and Berg (1956-7) — , metachromatic granules and metachromatic 

 plasm. But the anlagen of the top organs, e.g. notochord and neural plate, are 

 definitely the less metachromatic. 



The above cited facts lead us to think that these a-[i granules have more to do 

 with cellular life than with morphogenesis, which they only help by promoting 

 cleavage and early differentiation. The combined synthesis of acid mucopoly- 

 saccharides and acid phosphatase is probably their most significant feature; this 

 enzymatic equipment, which requires further investigation, is suggestive of 

 "lytic" as well as of "synthetic" functions. It is also interesting to point out that 

 numerous works on cellular localization of the non-specific acid phospho- 

 monoesterase in the cells or tissues have led their authors to the conclusion that 

 the enzyme must play a role in the "general metabolic processes of the cell" 

 rather than in the more specific cellular activities. In the actual state of knowledge, 

 a role in the digestion of yolk would be so far plausible; in the eggs of mammals, 

 which are deprived of yolk platelets, the same organelles would be mostly concerned 

 with the assimilation of maternal nutrient. 



Finally, when searching for a representation of the granules at later stages, or 

 even in adult tissues, one is bound to think of de Duve's lysosomes, to which the 

 author also attributes a role in intracellular digestion (1958). But there are 

 appreciable differences, e.g. the size of the elements, their intimate relationship 

 with mitosis. This interesting suggestion needs further exploration at both levels. 



The most evident feature of the chromotrope granules of the egg is their relationship 

 to the initiation of development and the beginning of cleavage. Thus, they must be linked 

 in some way with the progressive synthesis of DNA. Thanks to histophotometric measure- 

 ments, for which work on mammals is also advantageous, we have begun to learn the 

 steps in the synthetic process (Alfert, 1950; Dalcq and Pasteels, 1955; Vandekerckhove, 

 1959). If the mean somatic DNA content of the nuclei is assumed to be 2 units, the oocyte 

 nucleus has 4, the first polar body and the chromosome set of the second spindle (as far as 

 measurable) have 2, the second polar body and the young pronuclei have i each. Thus, 

 at the conclusion of the events of fertilization and maturation, the egg has a typical 

 diploid value of 2 units. These simple relationships have also been ascertained in a bean 

 wevil (Mulnard, 1954) and in a liver fluke (Govaert, 1957). 



Now, in rat and mouse eggs, it could be shown that from the i- to the i6-cell stage, 

 there is necessarily a doubling of the amount of DNA. This takes place quite early, that is 

 immediately after the telophase. The cells preserve their 4-unit value during the entire 

 intercinesis. Thus, some other process must influence the onset of mitosis, and must 

 prepare the quantity of DNA precursor which has to be available if there is to be a re- 

 cuperation of DNA. It is at this point that the a-[i system of chromotrope granules could 

 possibly play the role of a mobiliser of metabolic resources by its cooperation in digestive 

 activities. It has not been settled as to whether the chronological and spatial patterns 

 remain unchanged during the remainder of cleavage, or if there is a change in DNA 



