CONTENTS 



No. 1. JANUARY 



Robert W. Hegner. The relations between nuclear number, chromatin 

 mass, cytoplasmic mass, and shell characteristics in four species of the 

 genus Arcella. Forty-seven figures 1 



C. M. Jackson and C. A. Stewart. The effects of inanition in the young 

 upon the ultimate size of the body and of the various organs in the 

 albino rat. Five charts 97 



J. A. Dawson. An experimental study of an amicronucleate Oxytricha. 



II. The formation of double-animals or 'twins.' Twenty-two figures.. 129 



H. Saxton Burr. The transplantation of the cerebral hemispheres of 



Amblystoma. Nine figures 159 



No. 2. FEBRUARY 



II. V. Wilson and Blackwell Markham. Asymmetrical regulation in 



anuran embryos with spina bifida defect. Five figures 171 



Bennet M. Allen. The results of earliest removal of the thymus glands 



in Rana pipiens tadpoles. One figure 189 



Bennet M. Allen. The parathyroid glands of thyroidless Bufo larvae 201 



L. V. Heilbrunn. An experimental study of cell-division. I. The physi- 

 cal conditions which determine the appearance of the spindle in sea- 

 urchin eggs 211 



Caswell Grape. Amaroucium pellucidum (Leidy) form constellatum 

 (Verrill). I. The activities and reactions of the tadpole larva. Four 

 figures 239 



No. 3. APRIL 



Charles Howard Edmondson. The reformation of the crystalline style in 



Mya arenaria after extraction. Thirty figures 259 



Charles Zeleny. A change in the bar gene of Drosophila melanogaster 

 involving further decrease in facet number and increase in dominance. 

 Nine figures 293 



Harold Cummins. The role of voice and coloration in spring migration and 



sex recognition in frogs 325 



Henrt Laurens and Henry D. Hooker, Jr. Studies on the relative 

 physiological value of spectral lights. II. The sensibility of Volvox 



to wave-lengths of equal energy content. Two figures 345 



iii 



I (o=b(o o 



