1883.] immature Plumage of the North American Shrikes. 389 
Fic. 15. Cyclops tenuicornis infested with Distoma sp. ? 
“ 16. Simocephalus daphnotdes, sp. nov., head, 
“ 17. Ceriodaphnia reticulata, abdomen. 
"13 = head. 
“ 19. Léiliocryptus Sp., abdomen. 
“ 20. Cyclops tenuissimus, sp. nov., abdomen. 
21. - caudal stylet. 
“ 22. Cyclops tenuicornis (“ coronatus ”), end of antenna, 
“ 23. Scapholeberis armata Herrick, front view. 
n upper angle of abdomen. 
(To be continued.) 
to: 
A STUDY OF THE IMMATURE PLUMAGE OF THE 
NORTH AMERICAN SHRIKES, TO SHOW 
THEIR DESCENT FROM A COM- 
MON PROGENITOR. 
BY THOMAS H. STREETS, M.D. 
E is seldom that we find a group where the variations can be 
traced from the progenitors in an unbroken line through the 
whole series. Such a group we have in the shrikes of North 
America. 
Several years ago, before I had read the “ Descent of Man,” 
while studying the young of Suda cyanops, 1 was struck with. its 
close resemblance to the adult plumage of Sula leucogastra. I 
brought this fact to the notice of Mr. Robert Ridgway, the or- 
nithologist, and he showed me as a parallel case the young of the 
white-rumped and the adult of the great northern shrikes. I was 
Strongly impressed by these cases, with the importance of the 
study of the changes of the plumages of birds, as bearing the 
Same relation to their descent as the embryological changes of 
Structure which certain animals exhibit. Some years afterwards 
I found out that Mr. Darwin had fully investigated the subject. In 
the beginning of the chapter! where he discusses the immediate 
plumage of birds he makes the following statement : 
“When the young differs in color from the adult, and the colors 
of the former are not, as far as we can see, of any special service, 
they may generally be attributed, like various embryological 
structures, to the retention by the young of the characters of an 
early progenitor.” He states, in reference to the importance of 
“Descent of Man. Chap. XXI., p. 175. Amer. ed. 
