334 



PHYSIOLOGY AND MORPHOLOGY OF ANIMALS. 



Special Homology. — In suctorial insects the mouth 

 parts are an extreme adaptive modification — so extreme 

 in some cases that their homology with those of masti- 



Jkc- 



rnx- 



n 



Fig. 214. — Diagram showing the 

 relative positions and direction of 

 motion in mastication. The arrows 

 show the direction of motion. 



Fig. 215. — Side view of the head of 

 a grasshopper : e, eye ; other let- 

 ters are the same as in Figs. 212, 

 213, and 214. 



Fig. 216. — Head of a butterfly seen 

 from in front. The letters show 

 the same parts as in previous fig- 

 ures. 



catory insects is somewhat doubtful. We give what 

 seems the most probable view in two extreme forms: 



Butterfly. — In this case the labrum, Ibr, and the man- 

 dibles, m m (Fig. 216), are rudimentary and useless. 

 The maxillae, mx mx, are enormously elongated into 

 muscular hollow semicylinders, which, when put together, 

 form a long, flexible, hollow sucking tube. This is usu- 

 ally carried coiled up like a watch spring, but is uncoiled 

 and straightened when used as a proboscis for sounding 

 the nectar tubes of flowers, 



