THEIR REPRODUCTION (EGGS) 287 



whilst in a very small number the cock bird 

 alone performs the duty. We may also state 

 that amongst the wading birds the chicks re- 

 main in the shell for some little time after it 

 is cracked for their egress. 



But to return more particularly to the con- 

 sideration of the egg-shell. The texture, grain, 

 or surface of this requires a short notice. 

 This varies a good deal, and to some con- 

 siderable extent the peculiarities of its surface 

 are characteristic of certain groups. In a great 

 many species the grain of the shell is so 

 minute that the surface of the egg is more 

 or less highly polished, as in the case of the 

 Woodpeckers, reaching its greatest smoothness 

 in the curious eggs of the Tinamous. In the 

 majority of species the shell is comparatively 

 smooth, although in many a very minute grain 

 is visible even to the naked eye. In others it 

 is dull, somewhat rough and lustreless, as in the 

 Guillemot or the Sparrow-hawk, for instance. 

 In others yet again the surface is covered with 

 minute pits or pores, or grooves like shagreen, 

 reaching their highest development in such 

 Ratitae birds as the Ostrich and the Emu. 

 Then the egg-shell of various aquatic birds, 

 especially the Ducks, is peculiarly wax-like or 



