512 THE PHYSIOLOGY OF REPRODUCTION 



It is generally supposed that many syntheses occur in the 

 fertilised ovum, though direct evidence is difficult to obtain in 

 Mammals. In the chick haemoglobin is synthesised, and the same 

 almost certainly occurs in man and other animals, part of the 

 synthesis being effected by the trophoblast (see p. 505). The 

 nucleoproteins of the foetal cotyledons in the sheep appear to be 

 formed there, since they differ in composition from the nucleoproteins 

 of the cotyledonary burrs. The glycoprotein mucin is a characteristic 

 constituent of the intercellular ground-substance of the whole foetal 

 organism, and is apparently built up by the ovum. 1 The chondro- 

 proteins, a special group of glycoproteins, which yield on hydrolysis 

 proteins and the carbohydrate-containing chondroitin-sulphuric acid, 

 are also found chiefly in the frjetus as constituents of the cartilage 

 and tendons. 



A consideration of these and similar facts leads us to believe that 

 the new organism owes its development in large part to the energy 

 generated in it and by it from the combustion of substances supplied 

 by the mother, and to a series of active metabolic changes by means 

 of which these substances are transformed into living protoplasm. 

 Whether the nutritive materials are derived from the food or tissues 

 of the mother is of secondary importance. What is essential is that 

 the fertilised ovum obtains certain organic and inorganic compounds 

 and a supply of oxygen to carry out its work of organisation, just as 

 in the first period of extra-uterine life the growth and development 

 of the new being progress by its own activities, so long as it is 

 furnished with the proper materials. 



The special organ of embryonic nutrition is the trophoblast, and 

 evidences of its katabolic activities have been described in various 

 orders of Mammals. But in addition to procuring fixation of the 

 blastocyst to the uterine mucosa, and absorbing and katabolising 

 the food for itself and the embryonic portion of the ovum, it seems 

 also to possess anabolic fimctions, at least in the earlier periods of 

 pregnancy. Already developed in the blastocyst stage, it is active 

 .and functional for a considerable time. But in the later stages 

 it exhibits in all orders of Mammals a degree of morphological 

 degeneration which is incompatible with the maintenance of its 

 early physiological activity. It is further to be noted that its 

 condition varies inversely with the food requirements of the embryo. 

 When the daily requirements for the new organism are almost 

 infinitesimal, the trophoblast is well developed. But as the daily 



1 In the placenta of the cow, Jenkinson has described cells resembling 

 goblet-cells in the lining of the cotyledonary crypts, and ascribes to them a 

 maternal origin (Proc. Zool. *SW., London, vol. i., 1906). They may supply 

 mucin to the uterine milk, and so to the trophoblast. According to Assheton, 

 these lining cells are trophoblastic in the sheep. 



