ANIMALIZATION AND VEGETALIZATION
185
Various observations indicate changes in the superficial structures of
cells. In fertilized eggs of Paracentrotus lividus examination under darkground illumination shows an orange-yellow ring. At the 16-blastomere
stage, this ring covers the macromeres and the base of the mesomeres.
During gastrulation this pigmented material is completely invaginated when the entoderm forms. In eggs treated with lithium the pigmented ring is broader than in normal eggs and it is not wholly
invaginated. According to Runnström (1928a), who has observed these
phenomena, the orange-yellow ring is of lipoid nature. Other observations show that the properties of the superficial structure of eggs are
modified by lithium treatment. Studies on the deformation of centrifuged
eggs and of the effects of hypertonic solutions of lithium chloride or
sodium thiocyanate on eggs indicate that lithium ions increase and
thiocyanate reduces the cohesiveness of the superficial structure
(Lallier, 1955b). The changes in the elastic properties of cytoplasm
observed by Runnström (1935a) in eggs treated by lithium may be
due to an action on the cytoplasm and superficial structure. Moreover, the adhesiveness of the vegetal parts of embryos is increased by
vegetalizing agents, lithium, phenazone and chloramphenicol (Lallier,
1959c, 1961c). All these observations show that lithium, and other
agents active in embryonic determination, change the physico-chemical
properties of the superficial structure of cells.
The appearance of the cytoplasm is also modified. When examined
under dark-ground illumination, the cells of embryos treated with
lithium appear more greyish than the cells of normal embryos. Lithium
ions render the cytoplasm coarser (Runnström, 1928a; Lindahl, 1936).
When examined with the phase-contrast microscope, the cells of the
animalized larva appear darker than those of normal larva (Runnström,
1957). The higher density of the animal cells may indicate a higher
content of dry substance. The significance of these phenomena in the
experimental modifications of embryonic determination remains to be
determined.
Let us now examine the effects of animalizing and vegetalizing agents
on cellular inclusions. This analysis implies a preliminary study of the
inclusions in normal eggs. This problem has been approached with the
methods of classical cytology and by means of electron microscopy
(Afzelius, 1956, 1957a, b; Pasteels et al, 1958; Pasteels, 1959; Immers,
1960). In sea urchin eggs the structure of mitochondria follows the
traditional pattern. The mitochondria are partly associated with the
lipid droplets. The 'heavy bodies' are basophilic particles which may be
vitally stained by toluidine blue. Their granular content is enveloped by
a membrane closely similar to the nuclear membrane. The atypical
ergastoplasm has a vesicular structure; it is rich in Palade's granules.
185
Various observations indicate changes in the superficial structures of
cells. In fertilized eggs of Paracentrotus lividus examination under darkground illumination shows an orange-yellow ring. At the 16-blastomere
stage, this ring covers the macromeres and the base of the mesomeres.
During gastrulation this pigmented material is completely invaginated when the entoderm forms. In eggs treated with lithium the pigmented ring is broader than in normal eggs and it is not wholly
invaginated. According to Runnström (1928a), who has observed these
phenomena, the orange-yellow ring is of lipoid nature. Other observations show that the properties of the superficial structure of eggs are
modified by lithium treatment. Studies on the deformation of centrifuged
eggs and of the effects of hypertonic solutions of lithium chloride or
sodium thiocyanate on eggs indicate that lithium ions increase and
thiocyanate reduces the cohesiveness of the superficial structure
(Lallier, 1955b). The changes in the elastic properties of cytoplasm
observed by Runnström (1935a) in eggs treated by lithium may be
due to an action on the cytoplasm and superficial structure. Moreover, the adhesiveness of the vegetal parts of embryos is increased by
vegetalizing agents, lithium, phenazone and chloramphenicol (Lallier,
1959c, 1961c). All these observations show that lithium, and other
agents active in embryonic determination, change the physico-chemical
properties of the superficial structure of cells.
The appearance of the cytoplasm is also modified. When examined
under dark-ground illumination, the cells of embryos treated with
lithium appear more greyish than the cells of normal embryos. Lithium
ions render the cytoplasm coarser (Runnström, 1928a; Lindahl, 1936).
When examined with the phase-contrast microscope, the cells of the
animalized larva appear darker than those of normal larva (Runnström,
1957). The higher density of the animal cells may indicate a higher
content of dry substance. The significance of these phenomena in the
experimental modifications of embryonic determination remains to be
determined.
Let us now examine the effects of animalizing and vegetalizing agents
on cellular inclusions. This analysis implies a preliminary study of the
inclusions in normal eggs. This problem has been approached with the
methods of classical cytology and by means of electron microscopy
(Afzelius, 1956, 1957a, b; Pasteels et al, 1958; Pasteels, 1959; Immers,
1960). In sea urchin eggs the structure of mitochondria follows the
traditional pattern. The mitochondria are partly associated with the
lipid droplets. The 'heavy bodies' are basophilic particles which may be
vitally stained by toluidine blue. Their granular content is enveloped by
a membrane closely similar to the nuclear membrane. The atypical
ergastoplasm has a vesicular structure; it is rich in Palade's granules.