92 PROBLEMS OF EVOLUTION 



long-stalked kin. Fully developed crustacean appendages would 

 bring these sedentary degenerates into danger. 



FIG. 13. Balanus or Sessile Barnacle. A, external view ; B, anatomy ; a, antennules ; ad, 

 adductor muscle ; /, muscles of scuta and terga ; o, edge of parapet ; ov, ovary ; 

 ovi, oviduct ; sc, scutum ; sk, parapet ; t, tergum ; wo, female aperture. (From Parker 

 and Haswell's biology, after Darwin.) 



Worker ants have lost their wings, and as their business is to 

 forage, collect building materials, and attend the pupae, we may 

 well believe that it is an advantage to the community that they 

 should be wingless. Wings would encourage wandering aerial 

 habits, which would be out of place in those whose work is on the 

 ground and near at home. The young of many species of birds 

 are born helpless, and remain long helpless in the nest, quite 

 incapable of seeking food for themselves, but waiting open- 

 mouthed for their parents to feed them. Now 'it cannot be 

 doubted that the young of primitive birds were active from the 

 moment of birth as young lizards and young partridges are now. 

 But the advantage of helplessness is obvious when the nest is 

 placed so that a fall from it would be fatal before the acquisition 

 of the power of flight. We may assume, therefore, that there 

 was a great weeding out of those that were over-restless in their 

 babyhood. Even when the nest is on the ground, it is best that 



