I ORGANIZING ASPECTS OF GAMETO GENE SIS 319 



the polar bodies is not an activity limited to the pole, but a process involving the 

 whole egg cell, is immediately apparent in case of the Tubifex egg (Fig. ii). 

 The unfertilized eggs, according to the species considered, may remain in the state 

 of an oocyte with an unruptured germinative vesicle, may enter maturation (Fig. 1 9, 

 p. 328), or may expel one, or even both polar bodies before being fertilized. These 

 differences, more important than it may seem, need not be considered here. It should 

 only be emphasized that maturation does somewhat affect the cytoplasmic organi- 

 zation, with biochemical consequences and appreciable modifications of the cortex. 



II. INTRINSIC MORPHOCHORESIS 



Scientific progress sometimes necessitates a renovation of vocabulary. For several 

 reasons (Dalcq, 1949), it seems indispensable to include in one word the processes 

 of cell-division, cell-movements, internal and general transformation which 

 take place before the period in which cells or tissues efTectively become different in 

 their inner structure, metabolism and growth. The word morphochoresis will be 

 used here to describe these processes. The term is more or less equivalent to 

 "early morphogenesis", which will be reserved to more general situations. For 

 any particular part of the germinal system, morphochoresis may either result 

 mainly from inherent conditions, or be due to influences of other parts, often by 

 the mechanisms of induction. These different circumstances necessitate the dis- 

 tinction — again somewhat relative — between intrinsic and extrinsic, morphocho- 

 resis. A discussion of the latter is mainly reserved for our third subchapter (p. 357). 



For the sake of clarity, it seems advisable to use a terminology difTerent from the 

 usual one, but somewhat more precise. 



The conventional designations of animal and vegetal or vegetative poles should, 

 whenever possible, be replaced by pole and antipole. The three primary layers 

 of vertebrate embryos will be called ectoblast, chordomesoblast and endoblast, instead 

 of ectoderm, mesoderm and endoderm, which should be reserved for advanced or 

 adult stages. During the pregastrulation of birds and mammals, the two layers 

 will be called ectophyll and endophyll, instead of epiblast or primary ectoderm and 

 hypoblast or primary endoderm. During neurulation, the ectoblast will become 

 subdivised into neuroblast and epiblast; thus, the use of these terms immediately 

 tells that stages beyond gastrulation are being considered. 



In the analysis of experimental modifications of morphochoresis the words 

 norrnogenesis and paragenesis will also be used. The first term will suggest that the 

 fate of a germinal part has not been changed by the operation considered. The 

 second term will indicate the opposite result. Paragenesis may, or may not be, 

 oriented toward regulation. 



A. General trend and goal of intrinsic morphochoresis 



The realization of morphochoresis evidently results from some unfolding of 

 the properties acquired by the organized system. It is also pertinent that this 

 unfolding is not necessarily stereotyped, and that the system is able to cope with 

 situations imposed upon it by accident or by experiment. On the other hand, 



IJleralure p. 483 



