276 GEORGE W. BARTELMEZ 



although it is ahuost as apparent in the hen's egg as in the pigeon's.^ 

 The chalazal, better the ' long' axis, marks the axis of bilaterality 

 of the ovum as a whole; i.e., but one plane, that passing through 

 the long and polar axes divides it symmetrically. The evidence 

 for this is not only that one end of the long axis is definitely re- 

 lated to the embryo, but also that one end is morphologically dif- 

 ferent from the other as is shown below, p. 289. There are then, 

 two axes of symmetry in the incubated egg, one of the embryo, 

 the other of the mass of food yolk, which, though they do not 

 coincide, are definitely related to one another. Since the chalazae 

 are laid down very soon after the egg enters the oviduct, this rela- 

 tion must also exist at the time of fertilization. 



Evidence will be presented to estabhsh the following theses: 



1 . The bilateral symmetry of the ovum as a whole, manifested 

 by the long axis of oviducal and laid eggs, is present in ovarian 

 eggs at all stages of development from the primordial follicle on. 

 The long axis of ovarian eggs is the same as that of oviducal 

 eggs (p. 294). 



2. The antero-posterior axis of the embryo is predetermined in 

 the ovary because the axis of symmetry of the blastodisc of the 

 ovarian egg bears the same relation to the long axis of the entire 

 ovum as does the embryonic axis in the fertilized egg and in the 

 subsequent stages. 



It remains to be seen how much farther back in the Hfe history 

 morphological evidences of bilaterality can be found. The evi- 

 dence at hand points toward the view that bilaterality as well as 

 polarity are inherent characters of the protoplasm and persist 

 from generation to generation. 



1 Patterson's diagram ('09, p. 68) shows that he observed the long axis in the 

 pigeon and Sonnenbrodt ('08) and Riddle give two dimensions in their measure- 

 ments of oocytes in the hen but neither author attributed any significance to the 

 matter at the time. The relations do not seem to be so constant in the hen's egg 

 as in the pigeon's. Thus, in a series of over one hundred hen's eggs it was found 

 that in almost one-third of the cases the head of the embryo was directed toward 

 the observer when the pointed end of the egg was held to the right. This matter 

 deserves further study, for it involves the question as to whether the end of the 

 hen's egg that is to pass down the oviduct first is predetermined in the ovary as it 

 is in the pigeon. 



