2 4 2 THE POPULAR SCIENCE MONTHLY. 



condition of the remiges or quills, which never have coherent barbs, 

 and are therefore unfitted to the purpose of flight. In the ostrich and 

 rhea the bones, though comparatively small, are distinct and complete, 

 and the feathers large and definitely arranged. The emu, cassowary, 

 and apteryx show various degrees of degeneration, which apparently 

 culminated in the dinornis, no trace of a wing-bone of which bird has 

 ever been found. The question which naturally presents itself with 

 regard to these birds is, whether they represent a stage through which 

 all have passed before acquiring perfect wings, or whether they are 

 descendants of birds which had once such wings, but which have be- 

 come degraded by want of use. In the absence of paleontological 

 evidence it is difficult to decide this point. The complete structure of 

 the bony framework of the ostrich's wing, with its two distinct claws, 

 rather points to its direct descent from the reptilian hand, without 

 ever having passed through the stage of a flying organ. The function 

 of locomotion being entirely performed by powerfully developed hind- 

 legs, and the beak, mounted on the long, flexible neck, being sufficient 

 for the offices commonly performed by hands, the fore-limbs appear to 

 have degenerated or disappeared, just as the hind-limbs of the whales 

 disappeared when their locomotory functions were transferred to the 

 tail. This view is strengthened by the great light that has been thrown 

 on the origin of the wings of the flying birds by the fortunate discov- 

 ery of the Archaeopteryx of the Solenhofen beds of Jurassic age, as in 

 this most remarkable animal, half lizard and half bird, the process of 

 modification from hand to perfect flying bird is clearly demonstrated. 

 The three digits, which in the existing forms are more or less pressed 

 together and imperfect, still retain their freedom and complete number , 

 of phalanges, and are each armed with terminal claws, while the flight- 

 feathers and remiges of the cubital, metacarpal, and digital series are 

 fully developed and evidently functional. The earlier stages in which 

 the outer digits were still present, and the feathers imperfectly formed 

 or merely altered scales, are not yet in evidence. 



Some conception of the process by which a wing may have been 

 formed may also be derived from the study of the growth of feathers 

 on the feet of some domestic varieties of pigeons and poultry. 



MEASURING THE EARTH'S SURFACE. 



By FRANCESCO SANSOXE. 



f^\ EODETICAL science— that is, the particular branch of human 

 vIT" investigation which is devoted to ascertain what are the exact 

 form and dimensions of the earth — has not been slow to follow the 

 general progress. The advance made in this branch of studies since it 

 was first proved that the earth's form was spheric, and since Galileo 



