IV CONTENTS 



BRIDGES, CALVIN B. White-Ocelli An Example of a 



"Slight" Mutant Character with Normal Viability 231 



ISHII, O. Observations on the Sexual Cycle of the Guinea Pig. 237 



No. 5. MAY, 1920. 



JONES, D. F. Selective Fertilization in Pollen Mixtures . ... 251 



WODSEDALEK, J. E. Studies on the Cells of Cattle with Special 

 Reference to S per mato genesis, Oogonia, and Sex-Deter- 

 mination 290 



HEILBRUNN, L. V. Studies in Artificial Parthenogenesis. 

 III. Cortical Change and the Initiation of Maturation 

 in the Egg of Cumingia 317 



HAUSMAN, LEON AUGUSTUS. A Contribution to the Life 



History of Amoeba Proteus Leidy 340 



No. 6. JUNE, 1920. 



HYMAN, LIBBIE H. The Axial Gradients in Hydrozoa, III. 



Experiments on the Gradient of Tubidaria 353 



SHAFFER, ELMER L. The Germ-Cells of Cicada (Tibicen} 



septemdecim (Homoptera) 404 



