Vietnam or Thailand ? Vote for the TOP Country of the Week !
Updated: May 1, 2025
These variations occur because of a difference in chemical source and determination of the two instincts. While the ovary, stimulated by the thyroid and the adrenal medulla, is the chief determinant of the sex instinct, to the posterior pituitary must be credited the chief hormone of the maternal instinct.
Geoffrey Smith, one of the many promising young scientific investigators whose careers were cut short in the War, maintained views concerning somatic sex-characters different from that which explains their development as due to a hormone from the testis or ovary.
My conclusion is that the process of secretion set up by the mechanical stimulus of sucking is inherited as it was acquired, so that it only begins to take place in the individual in the absence of the hormone from the foetus, which was absent when the process was acquired.
This seems so very improbable that it suggests a doubt whether the same investigator was not mistaken with regard to the results of his experiments in transplanting gonads in Moths. Smith and Schuster conclude that the normal development of the thumb-pad depends on the presence of normal testes, but that there is no sufficient evidence that the effect is due to a hormone derived from the testis.
But in this case the sucking stimulus has been applied to the glands after a very short gestation, while the hormone from the foetus is being absorbed in the pouch, and therefore the hereditary correlation between secretion and absence of foetal hormone may be assumed to have been lost in the course of evolution. We have next to consider the question of the evolution of the corpora lutea.
Many physiologists in recent years have maintained that the testicular hormone is not derived from the male germ-cells or spermatocytes, but from certain cells between the spermatic tubuli which are known as interstitial cells, or collectively as the interstitial gland. They state that the interstitial cells appear in the male embryo before the gametocytes present distinctive sex-characters.
This shows that a hormone from the corpora lutea is not necessary either to the uterus or the milk glands, at any rate in the last third of pregnancy, though of course this does not prove that such a hormone is not necessary for the earlier stages both of pregnancy and growth of the milk glands.
The results of Steinach, if confirmed, would prove conclusively that the ovaries and testes produce hormones which determine the development of all the sexual characters, not merely physical but psychical. He adopts the view that the interstitial cells or gland are the source of the active hormone.
O'Donoghue, however, concludes from a study of the Marsupial Dasyurus that the stimulus which upon the milk glands proceeds from the corpora lutea in the ovary. In this animal changes in the pouch occur in pregnancy, which are doubtless also due to hormone stimulation, but which we will not consider here. Journ. Mic.
The plants in the rear quarter weren't sick they were dead. They were bleached to a pale yellow, like boiled grass, and limp. Nothing would save them now. "I'm a biologist, not a botanist " Jenny began. Hal grunted sickly. "Yeah. And I'm not a life hormone expert. But there's one test we can try." He picked up a pair of rubber gloves from a rack, and pulled off some wilted stalks.
Word Of The Day
Others Looking