58 ROBERT STANLEY McEWEN 
TABLE 1—Continued 
Restst= se. 11 12 13 14 lk 
Indices... 83.1 83.7 . 
Tests: soar 21 22 . 
Indicesee. 6628) (6556) “SIeSe 1G8i7—e SGl22) 16459 bSa. 15923 60NG 
MEStS: 3/1: 41 42 43 44 45 46 47 48 49 
Indices,2., 40-6) 5254), 49.9 = 5224) TAO Se 52.9) AS he sootoe aso 
43.0 
ing all the groups in each series. This was done by averaging 
the corresponding tests in each group of the same age and sex 
(table 1, graph 1). 
Fatigue curves for flies of different ages 
Average of seven cards of flies 4-6 days old 
ome, LO amie SO" ene ga Average of seven cards of flies 4-6 days old 
--..Average of five cards of flies 16-18 hours old 
++ ~Average of five cards of flies 16-18 hours old 
Per cent of phototropism 
Graph 1 
= a 
It appears that the younger flies are rather less phototropie, 
or at least less active, than those 4 or 5 days old. Also they tire 
more easily. Furthermore, although in the younger groups the 
females are consistently above the males, in the older groups the 
males, after the first few tests are quite the equals of the females. 
This result is substantially in accord with that obtained in my 
preliminary tests. 
