495 
Anatomy. — “On the relation of the first three cleavage planes to 
the principal axes in the embryo of Rana fusca Risel.” By 
Dr. H. C. DersMaN. (Communicated by Prof. VosMarr). 
(Communicated in the meeting of May 27, 1916). 
In this paper the results are given of some pricking experiments 
on the eggs of Rana temporaria, which I hope may contribute to 
the solution of various questions about which unanimity of opinion 
has as yet not been attained in spite of the numerous investigations 
on the earliest development of the amphibian egg. 
Starting point was the question: what becomes of the animal 
pole of the egg? It seemed very important to obtain an answer to 
this question in regard to a theory, worked out by me some years 
ago, on the evolution of the vertebrates from evertebrates (1913, 
a,b). The first principle on which this theory is based is that the 
invertebrate ancestor of the vertebrates must be sought among the 
Annelida, a suggestion which was upheld already half a century ago 
by Donry, Semper and by many others afterwards, and that the 
transition must be conceived to be such that the stomodaenm of 
the Annelida became the medullary canal of the Chordata. Since this 
last supposition is bold enough to endanger in some quarters the 
reputation of him who dares to put it forth (which I felt from the 
beginning), it was with great satisfaction that I found that nobody 
less than the discoverer of the neurenterie canal, KOWALEWSKyY, in 
1877 already had suggested a similar explanation, although less 
sharply formulated, when he wrote in a discussion on the homology 
of the nervous system in worms and chordates: ‘Die sonderbare 
3ildung des Nervensystems bei den Embryonen vieler Wirbelthiere 
(Amphioxus, Amphibien, Störe, Plagiostomen), bei denen Darm- und 
Nervenrohr ein zusammenhängendes Rohr darstellen, lässt uns ver- 
muthen, dass vielleicht solehe Thierformen existirten oder auch 
existiren, welche ein dem Nervenrohr der Wirbelthiere homologes 
Rohr besitzen, obgleich dasselbe eine andere Function erfüllt, dass 
es z.B. ein Theil des Darmeanals sei”. 
The second idea underlying the theory proposed by me is that, 
whereas in Amphioxus the whole of the medullary canal must be 
regarded as homologous with the stomodaeum of the Annelida, 
in the Craniota the praechordal part of the cerebral plate must be 
considered as having originated from the so-called apical plate 
of the annelid larva, the trochophora, by annexation of this latter 
by the medullary canal. Without enlarging upon. the different 
