Hyalella Knickerbokeri 249 
12. The number in a brood must increase each successive brood or 
as the animal increases in age. 
13. Hyalellae probably live a second summer, for the largest num- 
ber of broods occurring with ten to fifteen in a brood was toward the 
beginning of the season. (Figure 2.) 
14. Hyalella knickerbokeri is positively thigmotropic and nega- 
tively phototropic. 
15. The average number of young in a brood was 11.27 individuals. 
16. The largest number of broods produced were produced with 
seven in a brood. 
17. The maximum number in any brood counted was thirty young. 
18. The total number of young counted was 3,103. 
19. The total number of broods observed was 275. 
Acknowledgment. 
I undertook the studies recorded in this paper at the suggestion of 
Dr. Will Scott. It is due to his help that it is now completed. 
State Normal School, Terre Haute, Indiana. 
BIBLIOGRAPHY. 
Holmes, Samuel J., 700. Observations on the Habits and Natural 
History of Amphithoe Longimana Smith, Biol. Bull. Vol. 2, pp. 165- 
193. 
702. Observations on the Habits of Hyalella Dentata Smith. Amer- 
ica Morph. Soc. Science N. S. Vol. 15, pp. 529-530. 
703. Sex Recognition Among Amphipods. Bio. Bull. Vol. 5, pp. 
288-292. 
Jackson, H. H. T., 712. A Contribution to the Natural History of 
the Amphipod, Hyalella Knickerbokeri Bate. Bull. Wis. Nat. Hist. Soc. 
Vol. 10, pp. 49-60. 
Kunkel, B. W., 718. The Arthrostraca of Connecticut. Conn. State 
Geological and Natural History Survey. Bull. No. 26, pp. 1-180. 
Langenbeck, Clara, 798. Formation of the Germ Layer in the 
Amphipod Microdentopus gryllotalpa Costa. Journ. Morph. Vol. 14, 
pp. 301-336. fe 
Phipps, C. F., 715. An Experimental Study of the Behavior of 
Amphipods with Respect to Light Intensity, Direction of Rays and 
Metabolism. Biol. Bull. Vol. 28, pp. 210-223. 
Sexton, C. W. and Mathews, Annie, 713. Notes on the Life History 
of Gammarus chevreuxi. Journ. Marine, Biol. Assoc. Plymouth N. S. 
Vol. 9, pp. 546-556. 
Smallwood, Mabel E., ’00. Statistical Studies on Sand Fleas. Science 
Nees. VOlL-12)-p.<373; 
703. The Beach Flea, Talorchestia longecornis. Cold Spring 
Harbor Monographs. Pub. by Brooklyn Institute of Arts and Sciences. 
Valle, A. Della, ’98. Fauna und Flora des Golfes von Neapel. 
Gammarini. Vol. 20. 
Viré, M. Armand, ’03. Note Relative 4 Nourriture Des Niphargus 
Souterrains Bulletin Du Muséum D’Histoire Naturelle. Vol. 9, pp. 
279-280. 
Weckel, Ada L., 711. Fresh Water Amphipoda from Peru W. S. 
National Museum Proceedings. Vol. 38, pp. 623-624. 
