320 HUMAN PHYSIOLOGY 



almost entirely, what is left being called the umbilical 

 vesicle. 



(d) Secretions of the embryo. 



1. Meconium. Meconium is a dark brownish-green mass 

 having the consistency of pitch. It is found in the intestine 

 of the embryo, from which it is discharged soon after birth. 

 It contains 20-28$ solids, which include mucin, bile acids, 

 bile pigments (bilirubin and biliverdin, but no hydrobili- 

 rubin), cholesterin, fats, soaps. Substances in the faeces of 

 the adult which indicate intestinal putrefaction are lacking 

 in meconium. Meconium may be regarded as a solidified 

 secretion of the glands of the intestines, and its composition 

 indicates that the liver is the chief seat of its formation. 



The liver is formed early by diverticuli of the intestinal 

 wall in the form of the primitive liver ducts, which, by 

 branching, form the smaller bile passages. The liver secre- 

 tions take place as early as the third month. 



2. Formation of amniotic fluid. The amniotic fluid is 

 found in the amniotic cavity and surrounds the embryo. It 

 has a weak alkaline reaction ; its specific gravity varies con- 

 siderably, 1.002-1.028. It contains some proteids, salts, 

 urea, allantoin, and kreatinin. The amniotic fluid is formed 

 not only by the embryo, but also by the mother organism. 

 That part of this fluid is derived from the mother organism 

 is proved by the fact that sodium sulphindigotate injected 

 into the mother organism is found in the amniotic fluid, but 

 not in the embryo. Still the amniotic fluid is partly an 

 excretion product of the embryo, the urine of the embryo 

 being discharged into the amniotic cavity. 



In the development of the urinary organs, the pro- 

 nephros, or Wolffian bodies, are first formed. These are 

 glandular organs lying on either side of the vertebral column. 

 They are composed of coiled uriniferous tubules which 

 carry, at their closed end, a glomerulus and at the other 

 end, open into a common duct, the Wolffian duct. This 

 duct opens into the cloaca, wKose anterior end forms the 

 urethra by the formation of the perineum. Later on the 



