1 1 34 REPRODUCTION 



mechanism that the ferment which converts glycogen into dextrose 

 (glycogenase) is a?so either entirely absent from the liver earl}' in 

 gestation, or present only in traces ; and that as the glycogen-forming 

 and glycogen-storing functions of the organ increase in importance, it 

 becomes richer in glycogenolytic ferment. It cannot be doubted that 

 the glycogen found in the placenta is also deposited there in the 

 interest of the rapidly growing foetal tissues, perhaps as a kind of 

 current account on which they can operate at any moment of 

 emergency, when the more distant maternal reserves cannot be 

 drawn upon in time. The glycogen is formed in the placenta, prob- 

 ably from the dextrose of the maternal blood. By means of a 

 glycogen-splitting ferment, which can be extracted by glycerin from 

 the placenta, the glycogen appears to be reconverted into dextrose 

 for absorption by the foetus. In the earlier period of gestation the 

 placenta seems to perform vicariously the glycogenic function of the 

 liver, and as the glycogen content of the liver increases in the later 

 stages of intra-uterine life, that of the placenta diminishes pro- 

 portionally. 



The excretory glands of the embryo, except the liver, scarcely 

 awaken to activity during foetal life. Urine may indeed be some- 

 times found in the bladder at birth, but it is often absent. It is a 

 dilute urine, with a molecular concentration only about half as great 

 as that of the blood, and although a portion of the amniotic fluid, 

 which contains traces of urea and salts, in addition to smaU quantities 

 of albumin, may be secreted by the renal tubules, and find its way 

 through the still open urachus into the amniotic sac, this contribution 

 cannot imply more than a slight degree of glandular action. Under 

 certain experimental conditions, however, it can be largely increased. 

 Thus, extirpation of the kidneys in a pregnant animal causes an 

 increase in the amount of amniotic fluid (hydramnios) through the 

 stimulation of the foetal kidneys to increased activity by the passage 

 of the unexcreted urinary constituents of the mother's blood into 

 that of the foetus. After the injection of phloridzin into the foetus 

 sugar has been found in abundance in the amniotic fluid, although 

 the injection of that drug into the mother caused no such effect. On 

 the other hand, after injection of sodium sulphindigotate into the 

 circulation of the foetus in the sheep, the foetal kidneys contained 

 particles of the pigment, while the amniotic fluid remained un- 

 coloured. Long before full term the sebaceous glands have 

 begun their work by the secretion of the vernix caseosa, an 

 oily material which covers the skin and serves to protect it 

 from the continual irritation of the fluid in which the embryo 

 floats. 



The nervous system is even less active than the glandular tissues, 

 and not more active than the muscles. There is evidently no scope 

 for the exercise of the special senses. Psychical activity of every 



