being also the same, or as 1 to I of tin- latter, whilst the villi are the analogues 

 of tilt* villi is tin- intestinal canal, tho ono 1n'ing submerged in the sinuses, the 

 other in the juices in the intestine. Since the pumping action in respiration is 

 absolutely es-ential for compelling the comineive in tin' vessels, it follows that 

 this circumstance shmilil l)o represented in the t>mbryo,\i8 the maternal blood 

 (loos not enter the embryo, the latter feeding out of lEe sinuses simply by 

 menus of the villi in the pkoenta/and tliis pumping action spoken of ; for here, 

 as elsewhere in the Ixxly. there are no means for increasing circulation but by 

 rlii/tliiiu'rtil I'/HHt'ifx in fi-is.-iii-t'. The result must then be the action in the 

 plaeeiita simulating respiration. The relative frequency of this movement to 

 the action taking place in the f<etal heart is as 1 to 4, or the same as in respira- 

 tion. 



Tli i is. in the case of the placeutal souffle it is 30 to 35, and in the foetal heart 

 tho pulsations are from 120 to 140 per minute ; while, in the case of the air- 

 breather, the pumping action in the trunk or respiration is from 16 to 20, and 

 in the heart from fiO to 80 per minute. Again, tliis action in the placenta 

 servos not only to pump the tluids in and out of the sinuses, but at the same time 

 it also aspirates tho venous blood in the embryo for effecting oxygenation in it 

 the same as obtains in the lungs : the heart and vessels assisting in the one as 

 well as in the other, since it all forms a connected movement. We now see that by 

 reason of the great increase in pressure that obtains in the embryo, the action 

 in the organs for changing pressure is materially assisted, since the fluids flow 

 more readily in consequence. And here comes in the benefit of the 

 amniotic fluid, which not only increases pressure in proportion, but at the same 

 time it serves to transmit the force in the placenta and uterine walls to the 

 emlirvo for compelling corresponding changes in pressure upon the blood in con- 

 nection with the special functions. 



As illustrating this fact, .we see that when the placenta expands for aspirating 

 the tluids in the uterine sinuses, the organ advances into the uterine cavity, it 

 swells out and occupies more room, and, by thus encroaching upon the embryonic 

 area, it produces corresponding increase in pressure upon the liquor amnii and 

 omliryo, with low pressure in itself, which fulfils the conditions for increasing cir- 

 culation from the embryo to the placenta, at the same time, that it should aspi- 

 rate the fluid in the uterine sinuses. It could not do otherwise in the 

 very nature of things. During contraction in the placenta, the opposite 

 conditions should obtain, since this would determine high pressure in the latter 

 with low pressure in the embryo, the blood in consequence flowing through the 

 umbilical vein with augmented speed, and for the reason that contraction 

 should induce the volume of the placenta, which would inevitably reduce 

 pressure in the embryo in proportion, the blood flowing from one into the 

 other in conformity with organic law. To this, again, must be added the 

 action in the heart for aspirating the blood in the placenta. The media 

 in which the animal lives obviates the necessity for the extensive arrange- 

 ments for reducing pressure in the chest, which obtain in the lighter media 

 of the atmosphere, the heart, together with the force in the placenta and 

 umbilical vein, being sufficient for the purpose. 



