In tin- mantle, as \\vll as in the placenta, nnstri|>t-d miiM-l. ^ are present for 

 hflMMillg tin- .iiiT.i.'v nf tin- rhythmical expansions ami c. mil-actions. But 

 muscles arc nut essential in this action, a notable example nf which is 

 bnythed in tin- In-art itsi-lf, which expands ami cniitracts rt'gularlv and rhvth- 

 micallv liefon- a nniscl.- or m-r\.- is ili-\ -loped in tin- protoplasmic and un- 

 diH'en-ntiated \vallsip. -J'.l'.li, also in capillaries ami in earlv animal forms. 



It is interesting to note tin- fact in ttris connection i which has already been 

 comim-nt^l upon in tin- higher stages of ili-vdnpnicnt i. that <-r,ri/ ///<(.;/</ of 

 the animal, l.v rxtrinHni,' nr retract in.i; tin- mantle ami tin- Imincln-il ]K3dtlLcle8, 

 must ./'// increase circiilatimi ami n-spiration in roiTespnnilence. It could 



not In- ntherwi>e. Niiim-r..n- -tminita in tin- rounded extremities of the peduncles 

 (a, a, "i atl'onl fi-ci- in^i-i-ss mid ogress to the tlimls in the central canals (b,c). 



Fin. 2. MF.DI-SA (Rhtinntoma cuvieri). A, a, a, eight peduncles; 6, c, internal canals leading 

 up to the stomach; <l, stomach; e, e. <?, e, aurmountinj; ovarial sacs (four); /, k. lateral respi- 

 ratory canals; h, h, respiratory lobes on free margin of mantle (colored); I, I, thin membranous 

 l> trillions separating the caviiy of stomach from the ovarial sacs; i, i, external opening to 

 ovarial sacs; m, oesophageal passage. (After Grant) 



The capillary loops at the sides of the peduncles (/, k), which function as ab- 

 sorb-in; and respiratory vessels, may be taken as the simile of the capillary 

 hxips in the tufts of the placenta. 



This brief description will serve to explain the mechanical principle in the 

 placenta, and it now remains to be seen how this action is assisted by the action 

 takin j place in the womb itself ; or how the maternal and foatal circulations are 

 made to connect for effecting mutual interchange, the former supplying the 

 nutritive and force-producing elements for the growth and elaboration of 

 tissue, the latter yielding up the waste products to be borne back through the 

 maternal channels to the environment from which everything is derived, and 

 into w!iich, in due time, everything is returned in the form of waste 

 and tin il dissolution. 



