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ground that it is so long ago since the Vertebrata originated and 
nobody has witnessed the event and who would therefore be glad to 
see anatomy and embryology revert to the mere accumulation of facts 
without feeling any need for thoughts, to acknowledge that such 
a theory can occasionally lead to some good, as here to the state- 
ment of a new “fact”: the relation between the animal pole and 
the cerebral plate in the Craniota. 
The frog eggs were placed in a small glass-scale with water and 
cotton wool when in the 4- or 8-celled stage, after baving been 
freed from the surrounding jelly and under weak microscopical enlar- 
gement were pricked with the point of the spine of a hedge-hog, 
in such a way however that only a very trifling wound was made, 
which requires a fair amount of practice and patience. For at a 
somewhat more serious lesion a considerable extraovate is at once 
protruded, the size of which still increases during the subsequent 
cleavage and which results in abnormal development. For this reason 
similar experiments undertaken last year did not yield a single reliable 
result and made me doubt, as Scnurazr (1889) and H. V. Winson 
(1900) did, of the value of pricking experiments like these. But this 
year I had better luck. To be sure such trifling wounds have the 
disadvantage that often they soon heal entirely and that tke scab 
which is formed is east off, but the development is not interfered 
with in the least, the egg remains movable within the egg capsule 
and consequently can assume the position of equilibrium corresponding 
to each developmental stage. The resulis turned out to be very 
satisfactory, although occasionally eggs had to be rejected in which 
the mark was cast off too early. 
With eggs that had been pricked on the animal pole in the 4 or 
S-celled stage and during gastrulation had been repeatedly sketched 
by means of the drawing-apparatus, so that more or less complete 
series were obtained, I finally found the mark just in front of the 
anterior border of the cerebral plate. In four eggs | could follow 
the process so far without accidents such as the coming off of the 
marks and in all these four cases the same result was obtained. 
Elsewhere I hope to give reproductions of some of these series. 
This result is fully in accordance with what might be expected 
on wy theory. But it does not stand alone. With other amphibian 
species, particularly with the American frog Acris and the axolotl 
(Amblystoma), EyciesHymer made the same experiment as early as 
1895 and 1898 and in both these forms obtained exactly the 
same result. The mark here was found back either just in front of 
or upon or just behind the transverse head-fold. Not only in 
