ADAPTATIONS 431 



have short tongues armed on each side with barbs admirably 

 adapted for spearing larvae and dragging them from their 

 hiding-places. Still shorter is the tongue of the American " Sap- 

 sucker" {Sphyrapicus varius), and this is furnished with numerous 

 short hair-like processes on each side, near the tip, whose pur- 

 pose seems to be to draw up by capillary attraction the sap of 

 trees on which this bird largely feeds ; though with this juice 

 considerable numbers of insects, attracted by the flow of sap, 

 are also taken. 



The tongues of Humming-birds and " Honey-eaters " and 

 Sun-birds are even more remarkable. Owing to their small size 

 no slight skill is required to make out their structure, and much 

 of our knowledge on this subject is due to the Jabours of Dr. 

 Hans Gadow of Cambridge, and an American anatomist, Mr. 

 F. A. Lucas. They have shown that in the Humming-birds 

 the tongue is of great length and cleft for half its length. The 

 upper edges of the two branches curl inwards so as to form two 

 tubes. When the bird is engaged in extracting honey from 

 flowers this portion of the tongue is worked rapidly backwards 

 and forwards, and the juice which is forced by this means into 

 the tubes is withdrawn either by the formation of a vacuum at 

 the back of the mouth, or by pressing the tongue against the 

 roof thereof and so squeezing out the liquid. It is probable, 

 however, that this mechanism is devised rather for the capture 

 of insects which have gathered in the nectaries of the flower 

 than for the honey itself, inasmuch as large quantities of in- 

 sects are always found in the stomachs of these birds. But 

 the tongue of " Honey-eaters," such as the Australian and 

 Hawaiian honey-suckers, are more perfectly adapted for honey 

 gathering. Here the tip is cleft, and each branch may be again 

 split so that this organ terminates in four or eight small spiral 

 branches formed by the splitting up of each branch into hair- 

 like processes. This tip appears to have been derived from a 

 simple form wherein the edges of the tongue curled up to 

 meet one another in the middle line so as to form a tube as in 

 the Sun-birds of the Genus Hemignathus. Complex as these 

 honey-gathering tongues may be — though in no case is the 

 extraction of sweet juices the only function of the tongue — they 

 may all be derived from the typical avian tongue which at its 



