EARLY DEVELOPMENT IN THE FROG. 319 



characteristic structure of the Corymorpha stem." On removal 

 to water after several days in alcohol, a new individual arises 

 from the old tissue with its axis at right angles to the old one. 



Various investigators have observed that under certain condi- 

 tions, Hydra may lose its characteristic structure and "melt" 

 down into a shapeless mass from which a new individual may 

 arise. Dr. Hyman, in this laboratory, has recently observed 

 that such masses often give rise to several hypostome regions each 

 with tentacles. 



Physiological axiation begins, of course, with the origin of 

 polarity in the egg. Polarity may, conceivably, arise in several 

 ways. First, axiation and polarity may, as has been commonly 

 supposed, exist in protoplasm in relation to some intrinsic 

 molecular or other structure which is a fundamental property of 

 living matter; second, the primordial cell, from which the ovum 

 arises, may inherit its polarity, which, if true, merely pushes 

 the problem farther back; third, the appearance and position 

 of local differences in structural and functional order in the egg 

 protoplasm, that constitutes polarity, may arise during the 

 growth and development of the egg in response to conditions 

 external to it. The first alternative has been shown to be 

 untenable, and the second offers so little satisfaction, that, in the 

 light of the accumulated evidence, it seems necessary to consider 

 the last alternative as the more probable one, at least until it 

 has been shown that polarity arises in some other way. 



2. Origin of Polarity in the Frog's Egg. The mature egg of the 

 frog is described as possessing a radial symmetry about an 

 imaginary axis, the polar axis, passing approximately through 

 the centers of the pigmented (animal, apical) hemisphere and 

 of the unpigmented (vegetative, basal) hemisphere. This polar- 

 ity is marked by the localization of most of the protoplasm in the 

 pigmented hemisphere, by the eccentricity of the nucleus, and 

 by the distribution of pigment. In order to determine, if pos- 

 sible, whether, in the frog egg, a relation exists between its 

 polarity and conditions external to it, a study was made of the 

 ovarian relations of the egg, especially of the relation of the polar 

 axis to the region of attachment to the ovarian membrane and to 

 the blood supply of the egg. 



