138 A GUIDE FOR THE STUDY OF ANIMALS 



3. Of what use are the hooklets on the barbules ? 



4. State and explain the peculiar position of the shaft 

 of the primary feather ; of that of a contour feather. 



The plumage of many birds contains all stages of feather specializ- 

 ation, from down to pinion. Find as many of them as you can on your 

 specimen. 



5. What reason can you assign for the fluffy base and 

 the compact end of the contour feather? 



6. How much of the feather of a full-grown bird seems 

 to be supplied with blood vessels > How does this blood- 

 less or full-blooded condition affect the weight of the 

 feather ; of the plumage ; of the bird ? 



7. How would the above condition affect the tem- 

 perature of the blood and of the body .' Would it tend to 

 cool the animal or to conserve its heat ? 



8. Show how the air lying motionless amongst the 

 plumage may serve the same purpose as that in the pack- 

 ing of a fireless cooker or a " thermos bottle." 



9. How would the above condition affect the growth 

 and repair of the feather .' What connection has it with 

 moulting ? 



10. What kind of feathers forms most birds' "baby 

 clothes " .' What kind forms the adults' " underclothes " ? 



Suggested drawings. 



a. A typical feather. 



b. A feather of each kind. 



c. A bird with wings outspread, showing positions of 

 feathers. 



d. The minute structure of a feather. 



