304 GEORGE W. BARTELMEZ 



eggs ranged about 70 degrees. In the ovary of the* former many 

 oocytes were found in which the nucleo-cytoplasmic angle was 

 clearly 90 degrees or more, while the majority of the oocytes of 

 the other had an angle less than 90 degrees. This meager evidence 

 may be taken for what it is worth, for obviously the personal 

 factor might find expression through various channels in such 

 a study. Another possible line of evidence in this regard is the 

 study of the axis angles of the eggs laid by the offspring of a bird 

 previously studied. Experiments with this end in view are now 

 in progress. The heavy line B in diagram IV is a curve plotted 

 from the angles observed between the short axis of the blastodisc 

 and the long axis of the whole ovum, in stages previous to the 

 third cleavage. The similarity between the two curves makes 

 it practically certain that the short axis of the blastodisc is the 

 antero-posterior axis, especially when one bears in mind the large 

 body of evidence which goes to show that the anterior end of 

 the embryo is predetermined in the ovary. 



Three conclusions may be drawn from these observations on 

 axis angles: 



1. The essential feature of the relation between the embryo and 

 ovum as a whole is the fact that the embryo bears a different 

 relation to one end of the long axis than to the other. 



2. The eggs of a given bird vary much less as to their relation 

 between embryonic and long axes than do the eggs of different 

 birds. 



3. The short axis of the unsegmented blastodisc is identical 

 with the antero-posterior axis of the embryo. 



VII. DISCUSSION AND SUMMARY 



A. Bilalerality in vertebrate ova 



The fact that a fundamental character like bilaterality appears 

 during the ovarian history in so highly specialized a form as the 

 pigeon, suggests the possibility that in the vertebrates as in the 

 insects the antero-posterior axis of the embryo is predetermined 

 in the ovary. The suggestion is strengthened by the striking 

 manifestations of bilaterality which Conklin ('05) describes in 



