350 HIKOTA; ON THE SEKO-AMNIOTIC CONNECTION, 



On this a,cc(niiit the two kinds of germinuJ layers are differently 

 stained in the exti-;i -embryonic region. 



These differences are, however, not apparent in all cases. In 

 later stages, both the layers are intimately united and in some places 

 they can not l)e satisfactorily distinguished from each other. One 

 may even come to doubt whether the epiblastic bridge is replaced by 

 the mesoblastic tissue. Ikit I have many preparations in •which there 

 can not be any dou1)t on this point. For instance, in the sections 

 given in Figs. 71 and I'l, taken from the stage rei)reseiited in Fig. 6, 

 in which the epiblastic bridge has begun to be invaded by the meso- 

 blast, the one (Fig. 71) has the epi blast bridge still intact, while in 

 the other (Fig. 72), which comes behind the first, there is distinctly 

 no trace of the bridofe, althouo-h it must have existed here earlier. 

 The same state of things is observed in the case represented in Fig. 7 

 and Figs. 78-74. From these cases we may be certain that the 

 epiblastic cells have been entirely \\ithdrawn fi'om the prcAious bridge 

 and that the netted tissue is purely mesoblastic, as I have mentioned 

 in Section 5. 



That, near the posterior edge of the head fold of the amnion, an 

 epiblastic cell-mass is produced was observed by Schenk in 1(S71. 

 Of the fate of this mass he says : *' So bin ich geneigt anzunehmen, 

 dass die Zellen, welche die Verdickuno- ausmachen, l)is zum einem 

 bestinnnten bleibenden Theile derselben nach und nach in Liipior 

 Amnii aufgehen, und ihre Zerfallsprodukte scheinen zum guten Theile 

 an der Embryonalleibe ihre Verwendung zu finden." Th.\< inter- 

 pretation induced me to look carefully foi' the supposed processes of 

 dissolution, l)ut I have been unaljle to confirm his idea for the follow- 

 ing reasons. 



I have examined sections <jf nearly three dozen specimens of 

 embryos from the second to the tenth day of the incubation, and 



