248 Proceedings of Indiana Academy of Science 
time up to three days later when the mother moults in preparation for 
the next oviposition. 
Hyalella knickerbokeri swims about restlessly until it comes in con- 
tact with any object and then crawls into the crevices and between the 
branches of plants until as much of it is in contact as possible. There 
it comes to rest. H. T. Jackson (’12) says of this species that, ‘‘They 
may come to rest curled up in the surface film, the surface tension then 
producing the contact stimulus.” This may be easily observed at any 
time. 
PHOTOTROPISM. 
The influence that light has upon Hyalella is quite noticeable. If a 
number are placed in a glass dish, they collect almost immediately on 
the side of the dish away from the windows. There are always some 
leaving the light and swimming to the other parts of the dish but 
they eventually get back to the side farthest from the light. C. H. 
Phipps (715) says, the stimulus of the direction of rays to which the 
Amphipods react negatively has a stronger effect than the stimulus of 
light intensity.”” Thus we see Hyalellae are positively thigmotropic and 
negatively phototropic. 
The average number of Amphipods in a brood is 11.27 out of a 
total of 3,103 young in 275 broods counted. The maximum number in 
any brood was thirty young and the largest number of broods occurred 
with seven in a brood. 
SUMMARY AND CONCLUSIONS. 
1. Data collected seems to point to the fact that Hyalellae of north- 
ern Indiana have a distinct breeding season during the warmer months 
of the year. 
2. The breeding habits of Hyalella knickerbokeri are similar to 
other amphipods. 
3. The female is carried by the male from one to seven days before 
copulation occurs. 
4. The female moults before oviposition and the period between 
moults is twenty-four to twenty-six days. 
5. Copulation lasts about twenty-five to thirty seconds but is re- 
peated ten to twelve different times at intervals of a few minutes. 
6. Oviposition follows copulation in the following twelve to twenty- 
four hours. There are twenty-four to twenty-six days between ovi- 
positions, therefore there are twenty-four to twenty-six days between 
broods. 
7. The incubation period is about twenty-one days. 
8. The young are carried in the brood-pouch from one to three 
days. Then the female moults in preparation for her next oviposition. 
9. Preliminary measurements indicated that the length of the third 
joint of the peduncle of the second antenna is in direct proportion to 
the life length. 
10. The age of an amphipod is correlated directly with the number 
of young in a brood. 
11. The number in a brood increases as the length of the third 
joint of the peduncle of the second antenna. (Figure 1.) 
