THE ENGLISH SPARROW. 117 



although the term is commonly applied to the feathers projecting 

 from it. On its dorsal surface is a papilla bearing the opening of 

 the oil gland, which furnishes a lubricant for preening the 

 feathers. 



i) At the ventral junction of the uropygium with the trunk is the 

 transversely elongated cloacal aperture, a common external 

 opening for the intestine, the reproductive organs, and the urinary 

 excretions. 



THE PLUMAGE. An outer covering of feathers is peculiar to birds 

 alone. It is entirely a dermal structure. 



a) On examination it will be seen that the contour plumage is not 



uniformly distributed over the surface of the body, but springs 

 from certain areas called feather tracts, separated by featherless 

 spaces apteria. Find some of the latter. 



b) The quill feathers of the wing have been given special names. 



Those springing from the hand are the primaries. How many 

 primaries has the sparrow ? The secondaries arise from the fore- 

 arm, and tertiaries are sometimes present on the upper-arm. 



c) The feathers springing from the thumb constitute what is called the 



false wing. 



d) The shorter feathers overlapping the quills of the wings are the 



wing coverts. Notice the way in which the quills themselves 

 overlap and study the shape of the wing as a whole. Which sur- 

 face is the more convex ? What advantage is evident in this form 

 and in the method of overlapping of the quills ? 



e) Study the tail also with a view to determining its adaption to its 



particular work. Count the quills and note their mode of over- 

 lapping. Tail coverts overlap the bases of the quills above and 

 below. If opportunity offers compare the tail quills with those 

 of a woodpecker or a chimney swift. Special names have been 

 given by ornithologists to various tracts of the contour plumage, 

 but these will not be considered here. 



Exercise i. Draw a wing of the sparrow, dorsal view, partially extended 

 as in flight. 



