PHYLUM ARTHROPODA 



317 



actually forms of embryonic metamorphosis. Similarly the metamorphosis 

 of young into adults is a kind of delayed embryonic development. As 

 yet very little is known of the causes and forces involved in metamorph- 

 osis. The role of hormones in insect metamorphosis will be discussed in 

 the next chapter. 



145. Apis mellifera, the Honeybee 



As an example of a highly specialized insect the honeybee offers 

 interesting contrasts to the cockroach. Sense organs, mouth parts, wings, 

 legs and many internal organs are more diversified and specialized than 

 in the cockroach. The worker bee (Fig. 16.27), a sterile female, shows most 

 of these specializations. 



The most striking modifications on the head concern the mouth 

 parts. Labial palps and maxillae are fused into a sucking tube containing 

 a tongue formed from the middle portion of the labium. When this 

 tube is folded back against the body the short mandibles can still be 

 used as jaws, and the bee is thus one of the few insects that can both 

 suck and chew. 



The wings are small in relation to body size and have a much modi- 

 fied and reduced venation. The rear wing bears a row of minute hooks 

 that fasten to the front wing, forming a single flight blade. The round 

 and compact thorax houses powerful (light muscles. 



The legs have numerous modifications. The first tarsal segment of 

 each leg has a patch of bristles on its inner surface. Those of the first 

 and second pairs of legs are pollen brushes. The bristles on the tarsi 

 of the third pair of legs are arranged in regular rows forming pollen 

 combs. The tibia of the third pair of legs have a concave surface fringed 

 with curved hairs which forms a pair of pollen baskets. The lower inner 

 edge of each tibia has a row of stout bristles, the pecten, beneath which 

 the upper end of the first tarsal segment is expanded and fiattened to 

 form an auricle. 



As the bee visits flowers pollen sticks to its hairy body. This pollen 



I 



ne 

 Pecten-^ ^Auricle ^Pollen brush ^^^^^^ j 



Figure 16.27. The worker honeybee. (Adapted from Casteel.) 



