708 SUMMARY OF CURRENT RESEARCHES RELATmG TO 



this description that it would be inexact to speak of epiboly in connec- 

 tion with the egg of the Axolotl. While this diflfercntintiun has been 

 going on the gastrula has begun to bo invaginutcd ; the first sign of this is 

 the appearance of a broken line ; sections show that this lino is a groove, 

 and that it exists among cells not yet diftcrentiated, or, in other words, 

 at the dense pole of the egg. The lino takes the form of a horse-shoe, 

 and the two branches meet. In this way an invagination is produced ; 

 the segmentation cavity becomes reduced, and another cavity — which 

 will become the mesenteron — appears, and begins to put itself into rela- 

 tion with the invagination. The differences between this mode of 

 invagination and that which obtains in the Anura are pointed out. 



As there is at first no mesoblast along the axial line of the body, it 

 would seem that the notochord must be developed at the expense of tho 

 hypoblast ; and this is tho view of all embryologists who have written 

 on the question, with tho exception of Goette. But, a little later, the 

 medullary plates rise, and leave between them a rounded pad. Tho 

 interior of the egg is the seat of active work, and the result is that tho 

 mesoblast forms a continuous layer which passes below the axis. The 

 authors, therefore, are of Goette's opinion that the notochord of tho 

 Axolotl is of mesoblastic origin. To avoid any verbal dispute, in face 

 of the fact that the mesoblast itself is derived from the hypoblast, they 

 definitely state that the vitelline cells which give rise to the notochord 

 are first organized in the mesoblast, and do not form it directly. 



In anotlier communication * the authors state that in the segmenta- 

 tion of the egg there are 2, 4, 8, 24, 32, cells ; it was difBcult to follow 

 the segmentation later on. As to the fate of the blastopore which is so 

 various among the Urodela, they find that in the Axolotl it remains 

 always open, and becomes the definite anus ; there is no neurenteric 

 canal. 



Development of the Lamprey-t — Herr C. Kupffer reports the results 

 of his further study of the development of the lamprey. The material 

 was the result of artificial fertilization. Some ova kept at Konigsberg, 

 at a temperature of 8-10° C, developed into larvae on the 16-17th day, 

 while others kept at Naples did the same in 8 days. In both cases the 

 larvfe, when liberated, had reached the same stage, and measured 3 mm. 



In the formation of the blastoderm there is not an " overgrowth " of 

 one half of the ovum by the elements of the other. The outer layer of 

 morula cells acquires epithelial characters ; this begins, not at the ger- 

 minal or animal pole, but at the region which is subsequently dorsal. 

 This region appears along with the formation of a special keel or em- 

 bryonic shield. Gastrulation begins before the epithelial blastoderm has 

 quite surrounded the ovum. The blastopore appears at the posterior 

 border of the embryonic shield. 



The archenteron arises as a closed sac, with its dorsal wall directly 

 in contact with the ectoderm, though between them a group of smaller 

 cells is subsequently insinuated. These arise from the cells of the in- 

 vaginated margin, and are not to be regarded as mesodermic. They serve 

 for the caudal extension of the dorsal axial structures, and represent the 

 terminal bud in Teleostei, the sickle or terminal pad of Amniota. 

 Herr Kupfier proposes the term Teloblast. 



In the lamprey no neurenteric canal is formed, the blastopore is not 



* Loc. cit., pp. 282-4. t SB. K. Bayer. Akad. Wiss., i. (1888) pp. 71-9. 



