78 DR. J, W. JENKINSON OX THE [Feb. 6, 



columnar, but as the pits develop the lining cells lose their cilia, 

 become cubical, and exhibit a fatty vacuolation of their cytoplasm 

 (text-fig. 27 e). At no stage, however, in the formation of these 

 accessory cotyledons is the continuity of the cells lining the crypts 

 with the general uterine epithelium ever lost ; on this matter 

 sections of properly preserved material do not allow of a moment's 

 doubt. 



Whether the epithelium lining the crypts of the principal 

 cotyledons is also derived in like manner from the epithelium 

 covering the cotyledonary caruncles, is a point which can only be 

 definitely settled by an examination of the early stages of 

 formation of these organs. Apart, however, from the analogy of 

 the accessory cotyledons, strong evidence can be brought forward 

 in favour of such a view. In both the Cow and the Sheep the 

 epithelium lining the crypts, however much altered it may be, and 

 in the Sheep the alteration is very great, is still continuous at the 

 edges of the cotyledon with the unmodified epithelium outside : 

 this can be made out with the very greatest ease in the case of 

 even the oldest and largest cotyledons of the Sheep, not quite so 

 obviously in the Cow. In passing from the extra-cotyledonaiy 

 columnar cells (PI. Til. fig. 7) to the flat cells which line the 

 crypts, all transitional forms can be found uninterruptedly adjacent 

 to one another (text-fig. 28). The cells become cubical, then flat, 

 and finally extremely attenuated. Further, places may be found 

 in the crypts where this extreme alteration of the cells has not 

 occuri-ed ; small nests of cells were to be seen, particularly at the 

 summits of the crypt- walls and in the deepest portions of their 

 cavities, in which the cubical or even the columnar form is still 

 preserved ; and it is interesting to notice that it is from these 

 patches that new diverticula are given ofi" by the solid ingrowth 

 of masses of cells, in which a lumen is subsequently developed, 

 into the connective tissue below (text-figs. 29 «-e, p. 81). 



So far as my own knowledge goes, I am able to siipport fully 

 Kolster's contention that in the principal as in the accessory 

 cotyledon the crypts are lined by a secretory epithelium which 

 arises by modification of the cells which clothe the surface of the 

 non-pregnant uterus. 



2. The Histology of the Tro'phoblast. 



(a) The trophoblast consists in the extra-cotyledonary regions 

 of rather tall columnar cells ; the outer ends are protruding and 

 apparently amoeboid, the cells themselves, as Kolster and Bonnet 

 have recognised, decidedly phagocytic. At the bases of the villi 

 very tall columnar cells are found (PI. III. fig. 1), which are the 

 principal agents in the ingestion of extiavasated maternal red 

 corpuscles, as haemorrhage of the maternal capillaries takes place 

 most frequently at the summit of the walls separating the main 

 crypts. On the villi the cells are more cubical. It is noteworthy 

 that the foetal capillaries make their way into the trophoblast and 

 are often separated from the uterine lumen by only the thinnest 

 of cytoplasmic partitions. 



