SYMMETRIZATION OF THE EGG OF VERTEBRATES 59
symmetrization in this case. Does the mammalian egg behave as though
segmentation was total or meroblastic? Has it a unique mode of
symmetrization? The answer lies in the future.
V I I . Summary
The determination of bilateral symmetry in Vertebrates is achieved
through a reaction of the egg, the 'reaction of symmetrization'. This
reaction which fixes the plane of symmetry may be directed by several
factors. These directive factors (spermatozoon, rotation, gravity,
compression) have reversible effects; it is always the last one acting
before the reaction of symmetrization that is determining. When, in
normal conditions, the reaction of symmetrization starts, the plane of
symmetry becomes irreversible. The reaction of symmetrization is very
probably due to one or several important physico-chemical transformations of the egg and more especially of the cortex. It fixes the position
of the organizing centre. At present two types of eggs can be distinguished in vertebrates: eggs with early symmetrization, i.e., generally
speaking those in which segmentation is total, and eggs with retarded
symmetrization, i.e., those in which segmentation is discoidal. The eggs
in which symmetrization starts early fix their plane of symmetry before
segmentation starts, whereas in the other type, symmetrization is fixed
at the end of segmentation.
References
Ancel, P . a n d Calame, S. (1959). G. R. Acad. Sei., Paris 248, 893.
Ancel, P . a n d R a y n a u d , A. (1959). G. R. Acad. Sei., Paris 248, 1086.
Ancel, P . and R a y n a u d , A. (I960). C. R. Acad. Sei., Paris 250, 39.
Ancel, P . and Vintemberger, P . (1948). Bull. biol. Suppl. 31, 177.
Asmundson, V. S. (1931). Sei. Agric. 11, 662.
Banki, O. (1927). Verh. Anat. Ges., Jena 36.
Bartelmez, G. W . (1918). Biol. Bull., Woods Hole 35, 319.
Brächet, A. (1903). C. R. Ass. Anat., Liege.
Clavert, J . (1959). Arch. Anat. micr. Morph. exp. 48, 143.
Clavert, J . (1960a). Arch. Anat. micr. Morph. exp. 49, 1-22.
Clavert, J . (1960b). Arch. Anat. micr. Morph. exp. 49, 207.
Clavert, J . (1960c). Arch. Anat. micr. Morph. exp. 49, 345.
Clavert, J . (1961). Bull. Soc. Zool. Fr. 86, 381.
Clavert, J . and Filogamo, G. (1957). C. R. Soc. Biol., Paris 151, 1740.
Clavert, J . a n d Filogamo, G. (1959). C. R. Ass. Anat. 106, 165.
Clavert, J . a n d Vintemberger, P . (1954a). C. R. Soc. Biol., Paris 148, 376.
Clavert, J . a n d Vintemberger, P . (1954b). C. R. Soc. Biol., Paris 148, 1122.
Clavert, J . a n d Vintemberger, P . (1955). G. R. Soc. Biol., Paris 149, 413.
Clavert, J . a n d Vintemberger, P . (1957). C. R. Soc. Biol., Paris 151, 2183.
Clavert, J . a n d Vintemberger, P . (1958). C. R. Soc. Biol., Paris 152, 149.
Clavert, J . and Vintemberger, P . (1960). G. R. Soc. Biol., Paris 154, 400-
symmetrization in this case. Does the mammalian egg behave as though
segmentation was total or meroblastic? Has it a unique mode of
symmetrization? The answer lies in the future.
V I I . Summary
The determination of bilateral symmetry in Vertebrates is achieved
through a reaction of the egg, the 'reaction of symmetrization'. This
reaction which fixes the plane of symmetry may be directed by several
factors. These directive factors (spermatozoon, rotation, gravity,
compression) have reversible effects; it is always the last one acting
before the reaction of symmetrization that is determining. When, in
normal conditions, the reaction of symmetrization starts, the plane of
symmetry becomes irreversible. The reaction of symmetrization is very
probably due to one or several important physico-chemical transformations of the egg and more especially of the cortex. It fixes the position
of the organizing centre. At present two types of eggs can be distinguished in vertebrates: eggs with early symmetrization, i.e., generally
speaking those in which segmentation is total, and eggs with retarded
symmetrization, i.e., those in which segmentation is discoidal. The eggs
in which symmetrization starts early fix their plane of symmetry before
segmentation starts, whereas in the other type, symmetrization is fixed
at the end of segmentation.
References
Ancel, P . a n d Calame, S. (1959). G. R. Acad. Sei., Paris 248, 893.
Ancel, P . a n d R a y n a u d , A. (1959). G. R. Acad. Sei., Paris 248, 1086.
Ancel, P . and R a y n a u d , A. (I960). C. R. Acad. Sei., Paris 250, 39.
Ancel, P . and Vintemberger, P . (1948). Bull. biol. Suppl. 31, 177.
Asmundson, V. S. (1931). Sei. Agric. 11, 662.
Banki, O. (1927). Verh. Anat. Ges., Jena 36.
Bartelmez, G. W . (1918). Biol. Bull., Woods Hole 35, 319.
Brächet, A. (1903). C. R. Ass. Anat., Liege.
Clavert, J . (1959). Arch. Anat. micr. Morph. exp. 48, 143.
Clavert, J . (1960a). Arch. Anat. micr. Morph. exp. 49, 1-22.
Clavert, J . (1960b). Arch. Anat. micr. Morph. exp. 49, 207.
Clavert, J . (1960c). Arch. Anat. micr. Morph. exp. 49, 345.
Clavert, J . (1961). Bull. Soc. Zool. Fr. 86, 381.
Clavert, J . and Filogamo, G. (1957). C. R. Soc. Biol., Paris 151, 1740.
Clavert, J . a n d Filogamo, G. (1959). C. R. Ass. Anat. 106, 165.
Clavert, J . a n d Vintemberger, P . (1954a). C. R. Soc. Biol., Paris 148, 376.
Clavert, J . a n d Vintemberger, P . (1954b). C. R. Soc. Biol., Paris 148, 1122.
Clavert, J . a n d Vintemberger, P . (1955). G. R. Soc. Biol., Paris 149, 413.
Clavert, J . a n d Vintemberger, P . (1957). C. R. Soc. Biol., Paris 151, 2183.
Clavert, J . a n d Vintemberger, P . (1958). C. R. Soc. Biol., Paris 152, 149.
Clavert, J . and Vintemberger, P . (1960). G. R. Soc. Biol., Paris 154, 400-