68 ROBERT STANLEY McEWEN 
TABLE 8—(Concluded) 
DAYS 
GROUP 11 12 13 
tl fl tl. fi tl fl 
Pe pat ce Sere SI es od ee 113e3 22.9 27:3 
TUE, el a ae eerie es ean ar 25.0 22.6 
TEE eeu 58 ae Oe fa ai Re ge ea ES ee CO (TAR 4.3 
WB aed ci Se Rai a aii Pou aaicaee eae REA 
AVON ee ee ed Ca DOORS E SAME RA cork ee NP 
MOGAIS te tates a aii t escent 38.3] 4.3 | 45.5 27.3 
AN ETA GESTS kar: a4 i..c soa ato ean men van he oie 19.1) 4.3 | 22.7 27.3 
DifeETENCESaeen crxssieeen ie emer 14.8 220) 21nd 
with advancing age, it seems likely that this recovery represents 
nothing more than the usual increase. It should be noted that 
the usual index for unmutilated flies under this system of record- 
ing is from 30 to 36. This will appear in the next experiment. 
In this experiment, also under method I, five groups of flies 
were used. In the first group the wings were not removed until 
the sixth day after hatching, while in the fifth group they were 
removed on the day of hatching. The results were the same in 
every case. The insects showed the usual positive reaction to 
light until the day the wings were removed. At this point the 
positive reaction disappeared, the insects being indifferent to 
light and remaining substantially so for the rest of the tests. 
This occurrence was perfectly regular and very striking. It will 
therefore suffice to give only a couple of illustrations. In Group 
I there was only one fly. On the day after hatching, a t. |. in- 
dex of 30.4 was recorded. Its record was about this each day 
until the sixth, when the wings were removed. For the subse- 
quent five tests its average was f. 1. 1.7. On the sixth test it 
went up to t. 1. 4.7, but on the seventh it dropped to t. 1. 2 and-on 
the eighth and last the record was f. 1. 1. In Group IV there 
were five flies. On the day after hatching they averaged t. 1. 
33.4. The day following their wings were removed, one insect 
having been lost in the meantime. On this, the third day after 
