GASTRUL ATION AND EARLIEST DEVELOPMENT 179 



blastoporic rim first appears, i. e. about the egg equator 

 (ROUX's view), that consequently the embryo will lie entirely 

 on the lowei hemisphere of the egg but that the caudal 

 end does not, as ROUX thinks, extend on the other side 

 as far as the equator but no further than just beyond the 

 vegetative pole. The egg axis "n'est en relation avec aucun 

 des axes principaux de I'embryon" (1905). 



»As to the place where the dorsal lip first appears and 

 as to the extent of its progression over the surface of 

 the egg, opinions are also as yet rather divergent. PfluGER 

 and ROUX see the dorsal blastopore lip originate on the egg 

 equator, PfluGER allows it to travel through a distance of a 

 little over 90°, ROUX of 170- 180«, MORGAN and Ume Tsuda 

 (1894) see it originate + 30° below the equator and travel 

 through 120°. ASSHETON (1894) and KOPSCH (1900), with 

 whom IKEDA (1902) in the main agrees, also let it appear a little 

 below the equator (according to KOPSCH on an average 25°) 

 and move through a distance of 60 — 70° (ASSHETON) to 75° 

 (KOPSCH). BertacCHINI (1899) again quite agrees with 

 ROUX and estimates the distance travelled through a little 

 under 180°. KING (1902) finds in Bufo a displacement of 

 140° from a point below the equator. EycleshymeR gives 

 no definite data on this point, his opinon would probably 

 be in fair accordance with the results obtained by me. 



Conclusions from pricking experiments, — By carefully 

 watching the marked eggs and by drawing them repeatedly, 

 the above questions can of course be answered with cer- 

 tainty. The animal pole then furnishes the landmark which 

 most of the above cited authors did not dispose of ^). 1 

 have investigated in this way the eggs of Rana fusca, 

 Rana esculenta and Amblystoma tigrinum For both the former 

 species I have published my results in two preliminary 

 papers (1916). Those for Rana esculenta, however, need 

 certain corrections since further investigations have taught 

 me that part of the eggs on whose experiments my conclusions 

 weie based did -not develop in a normal way and showed a 

 certain tendency to the "spina bifida'' phenomenon. 



For the sake of convenience 1 begin with Rana fusca for 

 which my results are, most complete and reliable and which, 

 moreover, holds in a certain way an intermediate position 



') For the question whether the animal pole is indeed a perfectly 

 fixed point I refer to a remark made on p. 52 of the foregoing 

 chapter. For Rana fusca, at any rate, this may be assumed. 



