il46 PROF. J. p. HILL aKd Mr. r. h. buRNk on the 



the Lemuriforines and tlie Lorisiformes*, and as the outcome, we 

 know that all the true Lemurs are characterized by the possession 

 of the same non-deciduate, diffuse, epithelio-chorial type of 

 placenta, • which differs in the two groups and from genus to 

 genus only in comparatively unimportant though apparently 

 quite characteristic details, the general nature of which is 

 indicated in the following paragraphs (cf. also 17). 



Development is of the central type, and the entire mucosa of 

 the bicornuate uterus is involved in placental formation ; for, 

 though development begins in one of the uterine horns, and the 

 foetus, invested in its membranes, later occupies both that and 

 the body of the uterus, the chorionic sac sends a prolongation, at 

 any rate during the later stages of pregnancy (Milne-Edwards, 

 3; Turner, 5 ; Anthony, 12), also into the unoccupied or non- 

 foefcal horn, forming what we shall speak of as the chorionic 

 appendage. The uterine epithelium, immediately below which 

 are richly developed maternal capillaries, persists throughout the 

 gestation period, and is regarded both by Turner (5) and Strahl 

 (14) as being actively secretory. The uterine glands also persist 

 in an active functional condition. They mostly open in groups 

 in localised bare areas in the Leinuriformes (Milne-Edwards, 3 ; 

 Turner, 5 ; Strahl, 15), and in Galago among the Lorisiformes 

 (Strahl, 14), or their openings are more evenly distributed at 

 the bottom of the uterine crypts, as in Nycticehus (Hubrecht, 8). 

 The mucosa is always more or less markedly folded, the villous 

 outgrowths of the chorion fitting into the depressions or crypts 

 between the folds. 



The chorion is early established as a complete bilarninar 

 membrane enclosing the embryonal formation, and becomes 

 secondarily vascularised by the umbilical (allantoic) vessels as 

 the result of the early fusion of the outer wall of the allantois 

 with its inner surface. The chorion in this way is converted 

 into an allanto-chorion over the greater part of its extent. The 

 allantois is voluminous and multilobulate, covering the greater 

 part of the inner surface of the chorion ; and in later stages the 

 amnion is fused with its inner wall, the extra- embryonal coelom 

 being obliterated. The yolk-sac is early separated off as a com- 

 plete vesicle, appearing in later stages as a quite small flattened 

 sac (Milne Edwards, 3"& 4 ; Strahl, 14). 



The chorion, except over certain small restricted areas and at 

 its vaginal extremity, is produced into villous processes, which 

 amongst the Lemuriformes take the form of large laminar or 

 leaf -like folds, secondarily branched, or amongst the Lorisiformes, 

 of nodular processes. They are covered by a simple layer of 

 trophoblast (tropho-ectoderm), below which is a i-ichly developed 

 plexus of allantoic capillaries. These villous outgrowths fit into 

 complementarj' depressions of the folded surface of the mucosa, 



* See our reference list, in whicli tlie species studied have been noted under the 

 names of the investi era tors. 



