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as 'rneta-discoidal'. lt remains true, as Balfour pointed out, that 

 the placenta is only developed from a part of the area previously 

 vascularized by the capillaries of the umbilieal vessels; but his 

 views were clearly based on a misconception of the real nature 

 of the 'villi' in the human embryo. 



The exceedingly close similarity, which, as I have remarked 

 above, exists with respect to the foetal niembranes and placenta 

 between Tarsius on the one hand and Monkeys and Man on the 

 other, will be found, I believe to justify the separation of the 

 former from the Lemuroidea, of which sub-order it is at best a 

 very aberrant inember. The answer to the further question, whether 

 it is legitirnate on similar grounds to separate the Lemuroidea 

 from the Anthropoidea will depend very largely on the view we 

 take of the relation between the complicated forms of placenta 

 we have been describing, and the very slight connection which 

 exists between maternal and foetal tissues in the 'non-deciduate' 

 forms. In the latter, of course, the uterine epithelium never dis- 

 appears, and the foetal villi merely fit into uterine sockets from 

 which they are pulled out at birth. In the former there is in 

 most cases, very possibly in all cases, a preliminary degeneration 

 of the maternal epithelium ; and the placenta which is subsequently 

 formed consists of a trophoblast, permeated by lacunae containing 

 maternal blood (Insectivora, Rodentia, Tarsius, Monkeys and Man) 

 or by maternal capillaries the endothelium of which may (Cbeiro- 

 ptera) or may not (Carnivora) ultimately disappear, and vascularized 

 from the foetal side by the bloodvessels of the allantois; further, 

 as lias beeu repeatedly emphasised, it is not an ingrowth into 

 persistent maternal tissues, but an independent excrescence, para- 

 sitic upon them and eventually causing their degeneration. It is 

 not therefore, in the original sense of the word, a 'decidua' at all. 



Now, having regard to the affinity which exists, by way of the 

 Condylarthra, between the Carnivora and the Ungulata, it may 

 very plausibly be urged that in the 'angio-plasmode' of the former 

 we have the primitive type, which by the simple suppression of 

 the uterine epithelium may have arisen from, say, the diffuse 



