906 6 
Zoology. — “The Gastrulation of Rana esculenta and of Rana 
fusca’. By Dr. H. C. DersMAN. ‘Communicated by Prof. 
J. BOEKE). 
(Communicated at the meeting of November 25, 1916). 
In my note of May 27, 1916, I. was able to mention that 
similar pricking experiments to those described at that time for Rana 
fusca, were performed by me on the eggs of Rana esculenta also, 
an object, which in investigations on the earliest development of 
the frog egg we encounter much less frequently than the eggs of 
Rana fusca, which are to be obtained so much more easily. In some 
respects for pricking experiments like the present ones the eggs of 
tana esculenta appeared to me to offer advantages over the eggs 
of the other species, but on the other hand certain disadvantages 
are to be noticed, which in the latter are at least less conspicuous. 
Among the advantages it may be noted that in pricking, which in 
this case too was performed with the point of a hedgehog’s quill, 
one did not need to operate with nearly so much caution, to prevent 
the production of a voluminous extraovate, which has a disturbing 
influence on the further development. The egg content namely is 
in Rana esculenta far less liquid than in Rana fusca; indeed it is 
much more solid and tough, so that every prick not too clumsily 
made produces a little wound which in the last mentioned species 
can only be attained with the greatest caution and after several 
failures. Accordingly it was not difficult to apply to one egg 
several marks, e.g. one at the animal pole (a), and one or more 
at the crossing points of the third, equatorial cleavage furrow 
with the other, meridional ones, which, as in Fig. 1, we can 
indicate here again as 6 (dorsal), c (ventral) and d (the two lateral 
ones). Also the lighter colour of the egg has a great advantage, as 
it renders the surface images more distinct. On the reverse, the 
marks, so much more easily applied, also come off more easily, 
the wounds healing too soon. In not one of the eggs marked by 
me — all from one spawning — did it prove possible to rear them 
until the appearance of the medullary plate, without all the marks 
coming off beforehand. Next year therefore I hope to try and 
renew the marks in time during the development and thus to 
attain what this year was not reached. Yet the results reached 
until now seem to me sufficiently interesting to communicate them, 
and in completeness they are only a little behind those for Rana 
fusca. 
