442 THE PHYSIOLOGY OF REPRODUCTION 



to Driessen,^ its distribution in the placenta of the white mouse 

 before mid-term is the same as in the rabbit. It is in great 

 abundance in the decidual cells, especially in the boundary 

 layer between the maternal and foetal tissues. No glycogen is 

 found in the maternal endothehum, or in the foetal placenta. 

 Jenkinson ^ has studied the distribution of glycogen throughout 

 the whole period of gestation in the mouse. It appears first in 

 the cells which overhe the ectoplacenta, and increases in amount 

 till the twelfth day, when the mesoblastic processes are just 

 beginning to project into the trophoblast. Then the decidual 

 ceUs are disintegrated and the glycogen granules are mixed 

 with the detritus. Hence the hfe-history of the maternal 

 glycogenic tissue is shorter than in the rabbit. But in the 

 mouse glycogen again makes its appearance in the trophoblast 

 whidbi is most directly in contact with the maternal blood, 

 i.e. the part not penetrated by the allantoic capillaries. It Hes 

 in oblong ectodermal cells, which gradually encroach on and 

 occupy the space previously occupied by the maternal glyco- 

 genic cells down to the muscularis. Here the glycogen remains 

 till the end of gestation.^ 



According to Kolster, a considerable amount of, fat appears 

 in the decidua, in which the connective tissue and endothehal 

 cells undergo a fatty degeneration in the proximity of the giant 

 cells. No observations have been made regarding the meta- 

 bohsm of iron-containing substances. 



-Pig. — In the guinea-pig the ovum is again com- 

 pletely surrounded by decidua. Reichert* was the first to 

 notice that the ovum lay in a special cavity, " a httle nest." 

 Bischoff * stated that the nest was only temporary, and the 

 ovum again appeared in the uterine cavity, only that part of the 



' Driessen, "Ueber Glykogen in der Placenta," Arch.f. Gynak., vohlxxxii., 

 1907. ^ Jenkinson, toe. cit. See also Brit. Med. Jour., 1904. 



' Whether the differences in Ihe distribution o£ the placental glycogen 

 in the rabbit and the mouse during the later stages of pregnancy exist in 

 reality, or depend only on differences of interpretation, requires further 

 investigation. 



* Reiohert, " Ueber die Bildung der hinfalligen Haute der Gebarmutter,'' 

 Mailer's Arch., 1848. 



^ Bischoff, Entmcklung des Meeraohweinchens, 1852, 



