Twins is the name applied for two human bodies produced at a birth. Twins may be identical which often occurs as a result of a single ovum, or different in the case of multiple ova being fertilised. Research Twins
Alternate generation or metagenesis is that kind of multiplication, seen in some invertebrate animals or even in plants, in which parents produce progeny unlike, sometimes extremely unlike, themselves, while this unlike progeny give rise to others resembling the original forms. Sometimes there are more than one unlike form between these like forms. The Hydrozoa abundantly illustrate this phenomenon, also the Echinoderms, Polyzoa, Tunicata, the wheel animalcules, Nematoid worms, flat-worms, tape-worms, several of the true Annelids; among Crustaceans, Daphnia, the Phyllopods; among Insects, the plant-lice.
The steps may be seen in certain of the Hydroid Polyps, thus: (1) There is an ovum or egg, free-swimming and impregnated. (2) This ovum attaches itself to a fixed submarine object, and develops into an organized animal. (3) This organism produces buds or zooids, often of two kinds - one set nutritive, the other generative - unlike each other and unlike their parent, the whole forming a hydroid colony. (4) The generative set mature eggs, which on being liberated become the free-swimming ova (No. 1), and the cycle is renewed. A somewhat similar phenomenon is that of parthenogenesis. Research Alternate Generation
In biology, blastoderm is the germinal skin or membrane forming the superficial layer of the impregnated ovum, and from which the rudiment of the new being is formed. Research Blastoderm
In biology, blastomere is the term applied to each segment into which the ovum divides after impregnation. The segments may remain united as a single cell-aggregate, or some or all of them may become separate organisms. Research Blastomere
Spermatozoon (frequently shortened to 'sperm') are the male germ cells. In the lowest forms of life the spermatozoon and the female cell, or egg, are very similar, but in the higher forms the spermatozoon becomes a highly specialised active locomotor cell, and the female egg, or ovum, becomes a larger, more passive cell. The spermatozoon is provided with a head, body and tail, the head containing a nucleus of chromatin, the body the centrosome, and the tail is a cytoplasmic thread. The tail provides the cell with the power required for movement. Research Spermatozoon
The acrosome is a thin cap of protoplasm encasing the head of a sperm. The acrosome is believed to contain an enzyme, hyaluronidase, that dissolves the coronaradiata, the protective outer coat of the ovum, making sperm penetration easier. The enzyme of the acrosome of one sperm is insufficient to break down the ovummembrane. Therefore, contrary to popular opinion, it takes more than one spermatozoon to produce a baby. Only one sperm, however, will actually penetrate the egg. Research Acrosome
Aspiration is a procedure used to obtain eggs from ovarian follicles for use in in-vitro fertilization. The procedure may be performed during laparoscopy, using a long needle and ultrasound to locate the follicle in the ovary. For the procedure, the woman is given hormone medications to stimulate the ovaries so that several mature eggs develop. After 36 hours, an ultrasound scan is used to view and locate the eggs. Special software allows the health care provider to view one ovum at a time and helps guide the needle through the vaginal wall towards the eggs, called ova, for removal. Usually several ova are removed at one time. Research Aspiration
The Probert Encyclopaedia was designed, edited and programed by
Matt and Leela Probert
Abbreviations
Research Twins
