I 



FORMATION OF NOTOCHORD IN AMPHIBIA. 2Q/ 



der Deckzellen, vvelche zvvischen beiden Teilen des Mesoderms 

 liegen einander beriihren und sich auf der dorsalen Seite von 

 den aussersten Zellen abzuschniiren beginnen." In this way a 

 rod of cells is cut off from the inner layer of ectoderm to become 

 the notochord. I know of no other investigator whose results 

 agree with those of Perenyi. 



The results which Schwink (19) has obtained from his investi- 

 gations on Raua temporaries and Bufo vitlgaris are very similar 

 indeed to those which I have recorded in the present paper for 

 Rana palustris and Bitfo lentiginosus. According to Schwink, the 

 anterior portion of the notochord in Rana temporaria is entirely 

 mesodermal in origin, while the posterior part has added to it a 

 single layer of chorda-endoderm from the dorsal wall of the arch- 

 enteron, the endoderm cells at the side of the notochord growing 

 under and uniting in the mid-dorsal line. In Bufo vulgaris 

 Schwink finds that the dorsal wall of thearchenteronis composed of 

 deeply pigmented cells which, at the sides of the archenteron, pass 

 into the larger yolk cells, although he states that in some cases it 

 appears " dass die hier liegenden Entoblastzellen aus dem bisheri- 

 gen Verband scheiden um in den Mesoblast aufgenommen zu wer- 

 den." Concerning the formation of the dorsal wall of the arch- 

 enteron in the posterior part of the embryo Schwink states that, 

 " hier von beiden Seiten Darmentoblastzellen gegen die Mittellinie 

 streben und dass dadurch Zellen, die vorher den Darin dorsal 

 auskleicleten, mit zur Bildung der Chorda verbraucht werden." 

 This agrees exactly with what I have found to occur in the pos- 

 terior region of the embryo of Bufo lentiginosus. 



Brauer's (3) studies on the development of the Gymnophiona 

 show that, in the posterior region of the embryo, the upper wall 

 of the archenteron is at first formed of cells which have been 

 invaginated from the surface. These " animal cells " are sharply 

 marked off from the yolk or " vegetative cells " which form the 

 side walls of the archenteron. In the anterior part of the embryo, 

 the archenteron is extended by its connection with the segmenta- 

 tion cavity which is bounded entirely by yolk cells. At an early 

 stage of development, therefore, the dorsal wall of the archenteron 

 in the anterior region of the embryo is composed of vegetative 

 cells, while in the posterior region it is formed of cells invaginated 



