CONTENTS 
David H. Tennent 
Variation in Echinoid plutei. From the Biological Laboratory^ 
Bryn Mawr College. Twenty-four figures 657 
Duncan Johnson 
Studies in the development of the Piperacese. From the Bio- 
logical Laboratory, Johns Hopkins University. Seventy- 
one figures 715 
Robert P. Bigelow 
A comparison of the sense organs in Medusse of the family 
Pelagidae. From the Biological Laboratory, Massachusetts 
Institute of Technology. Thirty-eight figures. 751 
Ross Granville Harrison 
The outgrowth of the nerve fibre as a mode of protoplasmic 
movement. From the Sheffield Biological Laboratory, Yale 
University. Three plates and three figures 787 
George C. Price 
The structure and function of the adult head kidney of 
Bdellostoma stouti. From the Zoological Laboratory, 
Leland Stanford Jr. University. Four figures 849 
J. Frank Daniel 
Observations on the period of gestation in white mice. From 
the Zoological Laboratory, University of Michigan 865 
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