1906.] TLACENTA IN UNGULATES. 75 



and digested ; as a result pigment appears in the cells, while iron 

 can be demonstrated in the fluid in the uterine cavity. 



A recent examination of a fairly complete series of stages of 

 the placentation of the Cow and Sheep has enabled me to confirm 

 Kolster's valuable observations in all essential particvilars : the 

 secretion of cells in the viterine glands, the secretion and absorp- 

 tion of fat in the cotyledons (1 have never succeeded in finding 

 fat in the extra- cotyledonary uterus, though it is abundant in 

 the overlying trophoblast), the disintegration of large masses of 

 maternal tissvie, the extravasation of red corpuscles and their in- 

 gestion by the trophoblast with consequent formation of pigment, 

 the emigration of leucocytes through the uterine epithelium, — 

 certainly all occur in the manner described by this author. At 

 the same time there are one or two small points on which I am 

 unable to agree with him, such as the disappearance of the epi- 

 thelial cilia and the mode of formation of the accessory cotyledons ; 

 and others where his description or figures are deficient — the 

 histology of the trophoblast, for example. Farther, the pigment 

 was not examined spectroscopically by Kolster, and neither 

 Kolster nor Bonnet has paid the slightest attention to a highly 

 imjiortant substance, the glycogen of the placenta. Lastly, I have 

 made one or two interesting observations on the anatomy of the 

 " diverticulum allantoidis " and on the origin of the allantoic 

 bodies or hippomanes. 



My material includes pregnant uteri containing embryos of from 

 4 cm. to 60 cm. in length in the case of the Cow, from 14 cm. 

 long to full time in the case of the Sheep, of the after-birth foetal 

 membranes of the Cow, and non-pregnant uteri both virgin and 

 post-partum. 



The preservative fluids vised were aceto-corrosive, picro-corro- 

 sive, Flemming, and UO per cent, alcohol. It may be pointed out 

 that for the proper preservation of the maternal epithelial tissues 

 it is essential that the uterus should be pinned out, with the 

 overlying trophoblast and allantois, before it is placed in the 

 fixative. 



1. The Formation of Accessory Cotyledons. 



It is well known that in the Cow and Sheep the maternal 

 cotyledons ai-e formed in certain definite areas which can be dis- 

 tinguished in the virgin uterus (even of the unborn uterus) as 

 rounded prominences of the mucosa — the cotyledonary caruncles. 

 These caruncles consist of a dense mass of vasifactive sub-epi- 

 thelial connective tissue, and are covered by a columnar epithelium 

 continuous with that which lines the rest of the uterine cavity. 

 They contain no glands. 



After impregnation has taken place the caruncles are converted — 

 upon the attachinent of the blastocyst to the uterine wall — into 

 the maternal cotyledons, becoming pitted by the crypts in which 

 the fcetal villi lie. The number of cotyledons thus formed is 

 therefore predetermined and definite ; but in addition to these 



