THE COMMON TREE-WARBLER. 91 



The Tree- Warblers too have a more flattened 

 and flycatcher-like bill than the Willow Warblers' 

 (Phylloscopus), which, however, lay a totally 

 different type of egg from that which renders the 

 members of the genus Hypolais so remarkable. 



There are several species of birds which have 

 been variously placed by systematists among the 

 Thrushes or the Warblers, as, for instance, the 

 Nightingale and the Redstarts, which were for- 

 merly considered to be Warblers, but are now 

 reckoned as members of the TurdidcB, or family 

 of Thrushes. It may, therefore, be useful to 

 consider what are the characters which dis- 

 tinguish a Warbler from a Thrush — birds which 

 at first sight so closely resemble each other that 

 some of the tropical members of these two 

 families are difficult to determine by external 

 characters. The first point to be settled, then, 

 is the nature of the immature plumage of a 

 species, and it is a reply to the frequent exclama- 

 tions of wonder, that the British Museum should 

 find it necessary to keep such large series of 

 specimens of every species, that it is only by means 

 of such series, that the true history of a bird can 

 be learnt. To tell a Thrush from a Warbler, we 



