The germ-cell cycle in animals, by Robert W. Hegner.

Abstract

PAGE maintain that while protoplasm may appear to be fibrillar or alveolar, its essential basis consists of multitudes of minute granules. Wilson's view is the one usually adopted at the present time; that is, the protoplasm of the same cell may pass successively "through homogeneous, alveolar, and GERM-CELL CYCLE IN ANIMALS are not supposed to form part of the living substance; these are pigment granules, fat globules, excretory products, vacuoles (v) 9 etc. It has been found possible to explain many cellular activities and even the results obtained by experimental animal breeding by studies of the physics and chemistry of protoplasm. An exhaustive account of the subject is impossible and even unnecessary here, but the importance assigned to the physicochemical explanation of life phenomena requires a brief statement. Kossel has separated the cellular constituents into two main groups. (1) Primary constituents are those necessary for life ; these are water, certain minerals, proteins, nucleoproteins, phosphatides (lecithin), cholesterin, and perhaps others. (2) Secondary constituents are not essentially necessary and do not occur in every cell ; they are usually stored up reserve material or metabolic products representing principally what we have termed metaplasm. Water which constitutes about two-thirds of the animal is necessary for the solution of various bodies, the dissociation of chemical compounds, the exchange of materials, the removal of metabolic products, etc. Mineral substances are present in all animal tissues, and different tissues are characterized by the presence of different minerals. The principal ones are potassium, sodium, calcium, magnesium, iron, phosphoric acid, sulphuric acid, and chlorine. The other constituents are of a colloidal nature, and its richness in colloids is one of the chief charac-GERM-CELL CYCLE IN ANIMALS The principal poles are dissimilar ; the end of the egg containing most of the cytoplasm and nearer which lie the nucleus and centrosome is known as the animal pole ; the other end, which is often crowded FIG. 4. Germ cells. Ovarian ovum of a cat just before maturity. c. m. = cell membrane; mics. = microsomes; ncl = nucleolus; n. m = nuclear membrane; yk. al. = yolk alveoli. (From Dahlgren and Kepner.) with the yolk globules, is called the vegetative pole. The subject of the organization of the egg will be referred to more in detail later (Chapter VIII). The male sex cells or spermatozoa differ very strikingly from the eggs. They are usually of the of some of the principal types of life cycles we may select certain insects and coelenterates. A very simple life cycle is that of the wingless insects of the order APTERA. The young, when they hatch from the egg, are similar in form, structure, and habits to the fully grown individual and undergo no perceptible changes, except increase in size, until they become sexually mature adults. In INDEX OF SUBJECTS All numbers refer to pages. Words in italics are names of families, genera, species, or of higher divisions. Numbers in t...

Fusome topology and inheritance during insect gametogenesis

“…Across animals, sperm and egg develop within germline cysts whose cells are connected by arrested and stabilized cytokinetic furrows called intercellular bridges (ICBs) (Fawcett et al (1959); Fukuda and Hedinger (1975); Fuller (1998); Giardina (1901); Greenbaum et al (2011); Guo and Zheng (2004); Haglund et al (2011); Hegner (1914); Hegner and Russell (1916); Moens and Go (1972); Pepling et al (2015); White-Cooper et al (2009)). ICBs are conserved from insects to mammals, including humans, where they reveal the history of cell division and with diameters that are several microns large, ICBs are large enough to permit passage of proteins, mRNAs, and organelles (Greenbaum et al (2011); Haglund et al (2011); Imran Alsous et al (2018)).…”

“…An additional feature of developing Drosophila germline cysts is the presence of a membranous backbone known as the fusome, which replaces the mid-body-associated microtubules between cell divisions and fuses with the older fusomal material to form one continuous fusome, thus giving rise to a finger-like backbone that extends through the ICBs, connecting all germ cells (de Cuevas et al (1997); Grieder et al (2000); Lighthouse et al (2008)). First described in spermatocytes more than a century ago, the fusome has since been observed in numerous insects, where it is thought to be essential for fertility (de Cuevas et al (1997); Giardina (1901); Hegner (1914); Hegner and Russell (1916); Lin et al (1994); Mahajan-Miklos and Cooley (1994); Telfer (1975)).…”