Gaupp, Die Verwandtschaftsbeziehungen der Säuger usw. 21 5 



had a segmental origin. But as the figures which accompany 

 this paper show that conclusion can now be proved. In a Gull 

 embryo at the beginning of the second day as the anterior lip 

 of the blastopore is being carried backwards and the medullär}/ 

 folds are gradually rising somites are at the same time developed. 

 The first of these somites is that opposite the demarcation between 

 the second mesomere and the first rhombomere, and the next 

 five opposite rhombomeres i — 2, 2 — 3, 3 — 4, 4 — 5, 5 — 6, and the 

 beginnings of the next three segments are already indicated. 

 These segments with those previously mentioned are identical 

 in number, and I believe also in position, with those described 

 by Froriep in Torpedo. They have evidently been seen also 

 by Ussow 1 ), by Wilson and Hill 2 ), and by others. 



The conclusion is therefore that not only in Craniata but 

 in Chordata as a whole the growth of the dorsal lip of the blasto- 

 pore is characterised from the beginning with the formation of 

 the notochord and mesodermal somites, and that a definite number 

 of these latter are incorporated in the head of the Craniata. 



I have attributed to the mesencephalic flexure the changes 

 affecting the anterior portion of the head. Even during ontogeny 

 the flexure drags forwards the dorso-lateral structures, and presses 

 backwards, at the same time rotating downwards the ventral 

 parts. Phylogenetically the effect has been to bring the eye into 

 relation with the mesoderm of the orbit, which as has been seen 

 is to a large extent derived from a region below the hind bräin, 

 and to carry the mouth back to the region below the third^ rhom- 

 bomere with consequent atrophy or modification of the ganglia 

 and of the gills. The formation of the head of the Craniate is 

 therefore associated with the development of nerves and mesoderm 

 which have only a temporary embryonic existence, but which 

 point to an original segmental condition of the whole post-gastrular 

 that is to say the chordal region of the body 3 ). 



Es folgt der Vortrag des Herrn Prof. Dr. E. Gaupp (Frei- 

 burg i. B.). 



Die Verwandtschaftsbeziehungen der Säuger, vom Stand- 

 punkte der Schädelmorphologie aus erörtert 4 ). 



Von E. Gaupp (Freiburg i. B.). 



Mit 1 1 Figuren. 



Wenn ich es hier unternehme, zu einer brennenden Frage, 

 die schon so manche lebhafte Debatte hervorrief, der Frage nach 



x ) Ussow. Anat. Anz. Bd. 29. 



2 ) Wilson and Hill. Trans. Royal Society of London, vol. 199. 



3 ) Meek. Anat. Anz. Bd. 36. 



4 ) Der Vortrag ist hier im wesentlichen so wiedergegeben, wie er gehalten 



