Jackson, the Amphipod Hyalella Knickerbockeri.. 
49 
A CONTRIBUTION TO THE NATURAL HISTORY 
OF THE AMPHIPOD, 
HYALELLA KNICKERBOCKERI (BATE). 
Hartley H. T. Jackson. 
INTRODUCTION. 
The facts set forth in this paper result from experiments per¬ 
formed in the Zoological Laboratory of the University of Wiscon¬ 
sin and from observations made in various lakes and streams in 
Wisconsin. The original aim was an extensive investigation of 
the life history, behavior, habits and ecology of Hyalella, and a 
comparison of its activities with those of salt-water and land 
amphipods. The present paper, however, falls far short of this. 
The study was interrupted in February, 1910, by my moving to 
Washington, D. C., where material for the work was not avail¬ 
able, Hyalella? being notably absent in that region. Two efforts 
were made to import cultures from Wisconsin, but in each case 
without success. The study was undertaken at the suggestion of 
Dr. S. J. Holmes, to whom I wish to acknowledge my apprecia¬ 
tion for kind criticisms pertaining to the work. I also wish to 
express my appreciation of courtesies received from Professor 
George Wagner. 
Although Hyalella knickerbockeri is a common and widely 
dispersed species, comparatively little has been written concerning 
its general life history. Holmes (’02) contributed a brief paper 
upon the habits of Hyalella, and in two other papers (’oi,B ; 03) 
he discussed their phototactic reactions and their method of sex 
recognition. These three papers contain practically all that has 
been written concerning, the habits of this species in particular, 
though considerable work has been done upon the behavior of 
amphipods in general, the results of which are in many cases 
applicable also to Hyalella. In this connection I might mention 
the papers of Della Valle (’93), Gerstaecker (’oi), Holmes 
('’or,A), and Smallwood ('03, ’05). 
DISTRIBUTION AND HABITS. 
Hyalella knickerbockeri is found throughout the United States, 
from Maine to California and Mexico, and from Florida to 
