STUDIES IN MAMMALIAN EMBRYOLOGY. 631 



are as yet only somewhat enlarged. They are not the same enlarged tropho- 

 blast cells that were figured for Sorex on PI. XXXVII, fig. 27, vol. xxxi of 

 this Journal. The latter have become applied against the maternal tissue, 

 and have given origin to the ompbaloidean trophoblast. The shred of 

 omphaloidean trophoblast (o. T.) that is here figured gives ample indication 

 of active histolysis going on in this portion of the trophoblast. In the 

 preparation the shred here figured is not applied against any maternal tissue, 

 and its trophoblastic derivation is thus all the more indubitable. It is im- 

 portant to determine this, as it will be seen in Figs. 49 — 51 how eminently 

 difficult is the unravelling of maternal and trophoblastic tissue in the ompha- 

 loidean regions as soon as these two have become contiguous. 

 Utr. Mus. Cat. n°- Sorex 45 c, 2 r. 28 s. 



Fig. 49. — In this figure the trophoblastic annulus is rather less than more 

 distinct than in the former (cf. Fig. 7). The omphaloidean trophoblast is 

 undergoing a granular transformation simultaneously with degenerative 

 phenomena in the maternal tissues. 



Utr. Mus. Cat. n°- Sorex 42 e, 2 r. 14 s. 



Fig. 50. — The maternal tissue in partly degenerative resorption (cf. Fig. 8), 

 in consequence of the fusion with trophoblastic tissue. To the right strands 

 of epithelial tissue (s.) keep up the connection between the superficial and 

 the deeper maternal layers not indicated in this figure. These latter become 

 transformed into a new uterine epithelium (cf. Figs. 84 and 88). The fusion 

 between omphaloidean trophoblast and maternal tissue is very complete in 

 this preparation just above the upper rim of the trophoblastic annulus. The 

 hypoblastic nuclei are distinct. There are traces of blood-extravasate between 

 the trophoblastic annulus and the maternal tissue (cf. Fig. 84). 

 Utr. Mus. Cat. n°- Sorex 51 S, 2 r. 17 s. 



Fig. 51. — A yet earlier phase in the attachment of omphaloidean trophoblast 

 against the lateral maternal epithelial proliferation (cf. Fig. 5). A considerable 

 portion of the trophoblast has undergone a granular metamorphosis. Above 

 this there is another region where the distinction between embryonic and 

 maternal proliferated tissue is indeed impossible. In this stage a tropho- 

 blastic annulus is not yet even indicated. 

 Utr. Mus. Cat. n°- Sorex 73 c, 3 r. 13 «. 



Figs. 52 — 54. — Three regions of the placenta that was represented in 

 Fig. 32, more considerably enlarged. Fig. 52 from the lower, Fig. 53 from 

 the middle, Fig. 54 from the upper portion. The difference in size between 

 embryonic and maternal blood-corpuscles (the former being by far the larger) 

 renders distinction between maternal and embryonic blood-spaces very easy. 

 The preparation may be considered as a very perfect self-injection. The 

 maternal blood circulates in spaces delimitated on all sides by trophoblast that 

 is spread out to the utmost degree of tenuity. The embryonic blood circulates 

 in similar spaces, nowhere communicating with the former, and showing here 



