DEVELOPMENT OF THE FECUNDATED EGG. 507 



which here undergoes an hypertrophy ; it is moreover 

 characterized by the presence of both vascular and ramified 

 villi. These villi originating on either membrane are joined 

 together, interlace, and, finally, form the more or less circular 

 and apparently compact cake, which becomes the centre of 

 exchange between the maternal and foetal organism (Fig. 143, 

 20). 



Fig. 144. Diagram of the placenta! vessels.* 



An idea of the method of interchange between the mother 

 and foetus is represented by a diagram in Fig. 144. The 

 foetus receives and rejects the nutrient materials by means of 

 an osmotic interchange through the capillaries of each villus ; 

 this constitutes nutrition and respiration. 



The foetal respiration is effected by means of the placenta ; 

 we have already spoken of this form of respiration (see p. 

 324),. The necessity of placental respiration is, moreover, 

 supported by the serious accidents which result from suppres- 

 sion of the placental functions. When the circulation of the 

 cord which unites the placenta to the foetus (see foetal circu- 

 lation) is interrupted, the foetus perishes, not so much through 

 want of nourishment, as from a true asphyxia ; at birth pulsa- 

 tions in the cord cease only when the infant respires through 

 the lungs, because then the new method of respiration 

 definitely replaces that which has been accomplished by the 

 utero-placental connection. 



The nutrition of the foetus during the placental portion of 

 its life consists of an interchange of materials between the foetal 

 and the maternal blood through the placenta. Moreover, 

 the relations which combine both nutrition and respiration 

 are much simpler in the foetus ; the adult consumes materi- 

 als and transforms them into work (see Mechanical equi- 

 valent of heat, p. 78) or heat. The foetus has to perform no 



* 1, Uterus. 2, Intermediate tissue. 3, Placenta (membraiia reflexa seu 

 cacluca serotina), where the maternal and foetal vessels ramify. (Chailly- 

 Honore 1 .) 



