Hyalella Knickerbokeri 239 
A STUDY OF THE LIFE HISTORY AND PRODUCTIVITY OF HYALELLA 
KNICKERBOKERI BATE.! 
DONA GAYLOR. 
I. Introduction. 
II. Methods. 
III. Reproduction. 
1. Relation of reproduction to season. 
2. Time between broods. 
3. Distribution of size of broods. 
a. Relation of number in a brood to age. 
b. Seasonal distribution of number in brood. 
(1) The 10-15 maximum. 
(II) The 5-10 maximum. 
(III) The probable significance of these maxima. 
4. Additional observations. 
IV. Summary and Conclusions. 
V. Bibliography. 
INTRODUCTION. 
My first work with the arthrostracan crustacean, Hyalella knicker- 
bokeri Bate was in the summer of 1920 at the Indiana University Bio- 
logical Station at Winona Lake, Indiana, and its study was continued 
throughout the winter of 1920-1921. 
The first problem was to determine, if possible, the contribution 
made by Hyalella knickerbokeri Bate to the food of higher animals. I 
soon found I could not get very far in my studies until I had worked 
out the life cycle of the amphipod in some detail. 
Hyalella knickerbokeri is widely distributed. It is found in every 
state but at widely scattered localities. It is especially abundant in 
southern Canada, southern Minnesota, northern Iowa, Illinois, and In- 
diana. Miss Weckel (’11) extends its range to Lake Titicaca, Peru, 
South America. Its distribution is also discussed by Jackson (712), 
Weckel (’07), and Della Valle (’93). 
METHODS. 
Hyalella can be collected easily by washing Chara or other water 
plants in water contained in a small basin. They were then transferred 
to other vessels. The moving of individuals was done entirely with a 
small pipette and when the young were extruded they were transferred 
to a separate dish from that in which the mother was located, one at a 
time. It was next to impossible to count them when all together in one 
dish with the mother, due to the continual movement of all of them. 
Paired individuals were kept in separate dishes where they could be 
examined at will. The dishes were numbered and the data for each 
1 Contribution from the Zodlogical Laboratory of Indiana University No. 187. 
