404 THE PHYSIOLOGY OF REPRODUCTION 



epithelium proliferates so strongly that the cells cannot find 

 room in the wall, and tracts of them are invaginated into the 

 lumen. Later the cellular projections, sometimes along with 

 some of the underlying connective tissue as in the mare, are 

 cut off and added to the embryotrophe (Fig. 9.3). 



Traces of glycogen may be extracted from both the maternal 

 and foetal parts of the cotyledons, but it is too small in amount 

 to be demonstrated histologically. It is also present in small 

 amounts in the extra-cotyledonary areas — in the uterine 

 epithelium both superficial and glandular in the cow, in the 

 sub-epithehal connective tissue in the sheep, and in the uterine 

 milk (Jenkinson ^). Large quantities of glycogen are stored in 

 the plaques amniotiques, locahsed masses of cells on the internal 

 surface of the amnion, and later on the umbihcal cord. In the 

 calf embryo the plaques reach their full development about the 

 sixth month, and then gradually atrophy. 



It is obvious that the uterine milk must contain many 

 elements which have not been mentioned individually. The 

 product of conception requires numerous other substances 

 for its development besides protein, fat, carbohydrate, and iron. 

 Organic phosphorus compounds are furnished by the nuclei of 

 cells, and these may also contain iron. In general the fixation 

 of mineral elements is shght at the beginning of pregnancy, 

 but becomes active towards the end. But the requirements 

 vary at different periods of pregnancy. For example, sodium 

 decreases and calcium increases with the replacement of cartilage 

 by bone, and potassium increases with the increased manu- 

 facture of red blood corpuscles. These and many other sub- 

 stances are present in uterine milk though not demonstrated 

 histologically. Either they have been dissolved by the fixative, 

 or have remained unstained by the methods hitherto employed. 



One other constituent has been described by various ob- 

 servers, but its composition and significance are unknown. 

 Besides the leucocytes that contain pigment granules and fat, 

 others are filled with rod-like bodies, the " Uterinstabchen " of 

 Bonnet.^ Later they appear in the uterine milk. Rods have 



' Jenkinson, " Notes on the Histology and Physiology of the Placenta 

 in Vertebrata," Proc. Zool. Soc, London, 1906, vol. i. 



^ Bonnet, " Beitrage zur Embryologie der Wiederkauer gewonnen am 

 Sohafe," Arch. f. anat. u. Phys,, anat. Abth., 1884. 



