Hyalella Knickerbokeri 241 
carrying one individual through until the young were hatched. From 
the twentieth day until the twenty-fifth after ovipositoin he was com- 
pelled to be absent. On the twenty-fifth day the young were swimming 
about in the dish. Then, he says “From these observations we see that 
the eggs were in the pouch twenty-five days, at least, before they 
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2a. ie ay aaah ii Od We pass ¢. Bes amg amo Noe eh imeny Sel 
TUEGU-R Ey 
Figure 1. The ordinate represents the length of the third joint of 
the second antenna of the amphipod Hyalella knickerbokeri. The ab- 
scissa represents the number in a brood of the amphipods. There is 
shown a distinct correlation therefore between the age (since any part 
of an amphipod increases directly with age, the length of any part 
would represent the age) of an amphipod and the number in a brood. 
Bepenat 
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Gias 30° 
6-20320 
