Ch. VIII] PFLtJGER'S EXPERIMENTS 87 



remaining eggs there were eight in which the median plane of 

 the embryo made angles between 10 and 25 degrees with the 

 primary axis. In five cases the angle was between 25 and 45 

 degrees, and in two the angle was as great as 45 to 90 degrees. 

 Pilhger concluded that in abnormally turned eggs the median 

 plane of the embryo belongs to the system of meridians of the 

 primary axis of the egg, — as in normal eggs ; and that the 

 cleavage of the egg onl}^ breaks up the building material into 

 small building blocks, and it is of no importance in the subse- 

 quent stages of development how the splitting up has taken 

 place. 



Conclusions from the Experiments 



From the orientation of the embryo with respect to the pri- 

 mar}' axis in whatever position the egg may be, it might seem 

 that the material of tlie egg is not isotropic. That is to say, 

 the position of the embryo is fixed in the egg, and the embryo 

 assumes its predetermined position regardless of the method of 

 segmentation. A more careful examination will show however, 

 Pfliiger believes, that the egg is isotropic. 



It is obvious that although in most cases when the egg lies 

 with an oblique primary axis, the median plane of the body 

 belongs to the system of primary meridians, yet there are theo- 

 retically an infinite number of these meridians any one of which 

 might happen to be uppermost and to coincide with the median 

 plane of the body ; and Pfliiger's tables show that there must 

 be a great many possible primar}- meridians any one of which 

 may become the median plane of the embryo. 



In the second place, the dorsal lip of the blastopore never 

 develops on the upper hemisphere, however the egg may be 

 turned. Pfliiger says that, in all, he has probably examined a 

 thousand eggs, and never once found the blastopore above. It 

 appears always in the ivJiite heloiv the equator. Again, in an egg 

 abnormally placed the head always develops above and the body 

 heloiv. These relations could not exist for all positions of the 

 egg, if the position of the embryo were prefixed in its relation 

 to the primary meridians. 



Pfliiger considered one other possibility ; namely, that the 

 semi-fluid contents of the egg may rearrange themselves in eggs 



