308 
postulate for regressive, as has been shown for progressive 
development, a certain maximum amount of variation, the 
MONTGOMERY. 
passing of which would cause death. 
TA 
BLE XXI. INDIVIDUAL VARIATION IN THE NUMBER OF THE 
RECTRICES OF CERTAIN N. A. TETRAONID. 


NuMBER OF INDIVIDUALS 

She Sat EXAMINED. 
Centrocercus urophasianus 2a¢ : fo sae 
(Bonap.) 3 ae 19 ves 
[ iS 
I 
Dendrapagus obscurus (Say) 623,499, 2 (sex?) 
L 266,19 
1g 
D. obscurus fuliginosus I juv. 3 
Ridgw. 3 i on I (sex ?) 
466, gee 4 (sex ?) 
[ ie 
D. obscurus richardsonii 266, 4 (sex?) 
(Sab.) I*(sex ?) 
1¢ 



NuMBER OF 
RECTRICES. 
16 
18 
20 
16 
17 
18 

WIST’ . *-STITUTE OF ANATOMY AND BIOLOGY, 
PHILADELPHIA, Jan. 4, 1896. 

4 
c 
; 

