14 THE DESCENT OF THE PRIMATES 



ternal and the embryonic, have, during pregnancy, 

 developed parallel to each other, this interlock- 

 ing having simultaneously advanced step by step. 

 Fine maternal blood-vessels are distributed every- 

 where close under the surface of these maternal 

 cavities, and so the mother's blood which is laden 

 with fresh oxygen, thanks to the mother's breath- 

 ing, and with nutritive matter, thanks to the 

 mother's digestion, contains a full store of all 

 the necessaries which the embryo draws from it 

 by means of the peculiar arrangements on the 

 surface of the sac within which it is enclosed. 



The attachment between the sac and the 

 mother is nevertheless quite superficial ; they 

 remain permanently distinct and stand in the 

 same relation to each other as the hand does 

 to the glove which covers it, or as the rootlet 

 does to the damp soil into which it has pene- 

 trated. This latter comparison, taken from the 

 vegetable kingdom, is, however, in so far inac- 

 curate as it is often most difficult to uproot a 

 plant without tearing some of its rootlets, 

 whereas we may enucleate a Lemur-foetus out of 

 its mother's womb without as much as tearing or 

 displacing even a single cell. 



How entirely different these arrangements are 

 if we now come to consider the young Tarsius ! 



