AXr> 'I'lIE F(M^yrAL membranes, TX 'I'HE (""ITTOK. 



:;r)l 



hfive liecii ini;il)le to find :i single case like that represented in Fiii'. 4 

 of Schenk. On the conti'ary, the epililastic cell-mass seems to me to 

 have ;üwaA> a definite h(Minda,ry on the amniotic side. Often we find 

 il C(^aguhnn well stained with borax carmine, attached to the ('ell-mass, 

 but a similar coagulum is fonnd in other spaces, snc^i as the central 

 nervous canal, the alimentary canal,, and also in the coelomic cavity. 

 In Fig. (SS we see the cell-mass projecting into the amniotic cavitv. 

 and in Fig. 7(i the renmant of this projecting mass is I'epresented. 

 These are, however, extreme instances and in ordinary cases the cell- 

 înass. as a Abhole, is only slightly sunken into tlie amniotic cavit\- 

 (Fig. ()6). Such sinking into the amniotic cavity is not to lie wonder- 

 ed at when we consider the weight of the mass itself. 



As I have described in Sections 2 and 5, the epiblastic cell-mass 

 is being ^constantly foi-ined and constantly removed from the very 

 beginning of the formation of the connection, and being situated near 

 the free edge of the head, fold, the product of its dissolution, if it wei-e 

 actually dissolved, would diffuse wddely through the surrounding 

 albuminous fluid, and but little'of it be mingled with the amniotic 

 fluid, which is speedily increased in volume, evidently from othei- 

 sources. 



Finally, from the physiological point of view, it seems to me to 

 be improbable that the epiblastic cells dissolve nj) for the use of othei" 

 epiblastic cells of the same surface. 



From the preceding discussion, and from the fiict that from an 

 early stage of folding the deltoid cell-mass is constantlv added to at 

 the posterior free edge and constantly reduced neai- its anterior apex, 

 it is probable tliat the cell-mass is used u]) foi- the extension of the 

 surface of the fold, and not for any otlicr special pui-pose. It is, 

 besides, a noteworthy fact, that in Chelonia tlie deltoid area is not 

 thickened dorso- ventral ly -iiid undergoes, of course, no dissolution. 



