912 
detaching themselves, yet it may be stated already that the closing of 
the blastopore here does not occur, as in Rana fusca, diametrically 
opposite the animal pole, but more to the dorsal side. So the appear- 
„ance of the medullary plate in this egg was not observed anymore 
before the detachment of the marks, just as little as in the other 
eggs. Now, however, it does not rarely occur, that in eggs, where 
Fig. 7. Another egg, with foundation of medullary 
plate. + a and 6 as transferred from fig. 6. 
the blastopore has not yet quite closed, the first rudiment of the 
medullary plate becomes visible already. Such an egg is represented 
e.g. in fig. 7, where we see that the foundation of the embryo 
does not, as in Rana fusca, encircle nearly 180° of the egg, but is 
somewhat shorter. If now we hold up to the light this drawing 
together with that of fig. 7 and we transfer to fig. 7 the position 
of the marks « and 5 from tig. 6, it appears that they find them- 
selves at exactly the same place as we stated in Rana fusca, i.e. 
respectively just in front of the transverse head-fold and at the 
transition of ceredral and medullary plate (fig. 7*). The objection 
might be raised that the possibility is not excluded, that during 
or before the appearance of the medullary plate there might 
still occur cell wanderings, which would raise doubts as to the correctness 
of the above conclusion. As we have seen, however, that in 
Rana fusca there is no question of anything of the kind, we may 
safely assume the same in this case. So this result for Rana esculenta 
again confirms the conclusions drawn from the theory which has 
engendered the present investigations. | 
