GAMBETTA, LEON-MICHEL. - French politician, b. Apr. 2, 1838 at Cahors, d. Dec. 31, 1882 at Ville-d’Avray (Seine-et-Oise). Descended from a Genoese family settled in France at the beginning of the century, G. took up the legal profession in Paris and revealed himself as an orator before the general public during the trial of the Réveil.
The editorial staff of the Réveil had been brought before the judicial authorities for having promoted a subscription for a monument to a deputy who had fallen on the barricades in 1851 while opposing the coup d’état of the future Napoleon III. Against the Napoleonic Empire, G. was a determined representative of republican opposition. After the fall of the Second Empire, he ardently collaborated in consolidating the Third Republic, promoting a
(properly Doc. Castel)
GAMETES AND GAMETOGENESIS — Fig. 2. Spermatic: a) Triturus; b) Nereis (annelid); c) Guinea pig; d) Phyllopaneus (bird); e) Man; f) Bat; g) Castrada (turbellarian); h) Porcellio (crustacean); i) Lobster; l) Ascaris (nematode).
In the germinal line, and sometimes even at the two-cell stage (blastomeres), the cell that will give rise to the gametes can be identified; but more often, as in mammals and man, such a distinction is not discernible early on.
Gametes may be of one type (isogamy) or of two types (anisogamy), distinguishable by their behavior (physiological anisogamy) or, as in most cases, also by their morphological appearance. In this case, there are male gametes or spermatozoa, and female gametes or eggs. If the difference consists only in size, they are referred to as macrogametes and microgametes. While in cases of physiological anisogamy all gametes are motile, as in isogametes, being provided with flagella that allow mutual encounter for the constitution, through the act of copulation, of the zygote (v. FERTILIZATION), in the case of morphological anisogamy there is a motile element, the sperm, and an immotile element, the egg. This difference is related to the egg’s initial accumulation of a certain quantity of reserve substance, the yolk or vitellus, which will serve the energetic needs of the embryo in the early stages of development. The accumulation of yolk is more or less abundant in various animals in relation to their specific ecology and that of their juvenile forms (depending on whether the eggs are laid in water or on land, the duration of embryonic life, the presence or absence of a larval stage, etc.); therefore, the size of the eggs varies greatly among different animal groups.
Based on the quantity and distribution of yolk, eggs are said to be oligolecithal or alecithal if, like the human egg, they are poor in yolk and thus very small; they are said to be telolecithal if there is an abundance of yolk. These in turn are distinguished into: telolecithal oligolecithal, if the entire egg undergoes segmentation (as in amphibians); telolecithal meroblastic, if segmentation is partial, while the yolk mass remains unsegmented at one pole of the cell (as in elasmobranchs, reptiles, and birds); a particular case of this type of egg is the centrolecithal egg of arthropods, in which the yolk, after segmentation, accumulates at the center of the egg (fig. 1).
The egg may have only its own cell membrane (alecithal eggs) or additional membranes and shells added during passage through the maternal oviducts (cleidoic eggs).
The spermatozoon or sperm, on the other hand, is characterized by its motility. It is a very small cell consisting of a head, which contains the nucleus, an internal dicotylastratic piece, and a very long tail that serves as a propulsive organ. In the head, there is also a cytoplasmic organelle, the acrosome, often shaped in a characteristic pointed manner, called the perforatorium; sometimes, in addition to the flagellated tail, there is also a more or less extensive undulating membrane.
The spermatozoa of various animal species have typical structural characteristics by which they can be distinguished (fig. 2). In addition to these typical flagellated spermatozoa, there are those without flagella, whose movement occurs through pseudopodia or characteristic extensions, such as the amoeboid movement of certain worms, or those with various appendages found in many crustaceans (fig. 3). There are also cases of immotile spermatozoa that are taken up by the eggs through pseudopodia.
The process of development of gametes into spermatozoa or eggs capable of fertilization is called gametogenesis, which is therefore distinguished into spermatogenesis and oogenesis (fig. 3).
The primordial germ cells, not yet differentiated into male and female cells, are called protogonia; they are defined as spermatogonia and oogonia when the subsequent production of spermatozoa or eggs is identified. After a period of multiplication of spermatogonia and oogonia, of more or less long duration (and which for oogonia is generally much shorter), the cells enter a period of growth and are called primary spermatocytes and primary oocytes. At the end of growth, which is brief for spermatocytes and longer for oocytes, and during which vitellogenesis occurs, they pass into the stage of primary spermatocytes and primary oocytes. From this stage, the maturation period begins and continues.
Based on the stage of the spermatocyte of the cells of the testis, in which the nucleus is located, an internal dicotylastratic piece, and a very long tail serving as a propulsive organ. In the head, there is also a cytoplasmic organelle, the acrosome, often shaped in a characteristic pointed manner, called the perforatorium; sometimes, in addition to the flagellated tail, there is also a more or less extensive undulating membrane.
The spermatozoa of various animal species have typical structural characteristics by which they can be distinguished (fig. 2). In addition to these typical flagellated spermatozoa, there are those without flagella, whose movement occurs through pseudopodia or characteristic extensions, such as the amoeboid movement of certain worms, or those with various appendages found in many crustaceans (fig. 3). There are also cases of immotile spermatozoa that are taken up by the eggs through pseudopodia.