XII 



PHYLUM CHORDATA 



479 



time, in a rough nest, and are incubated or sat upon by the 

 parents for fourteen days, the temperature being in this 

 way kept at about 40 C (104 F.). At the end of 

 incubation the young Bird is sufficiently developed to break 

 the shell and begin free life. It is covered with fine down, 



Lod' 



el9 



FIG. 273. Columba livia. Male 

 urinogenital organs. adr, ad 

 renal ; cl.2, urodaeum ; c/,j, proc- 

 todaeum ; k. kidney ; ts. testis, 

 that of the right side displaced ; 

 ur. ureter ; ur '. aperture of 

 ureter ; vd. vas deferens ; vd '. its 

 cloacal aperture ; 7>. s. vesicula 

 seminalis. (From Parker's Zoo- 

 tomy.) 



ur 



FIG. 274. Columba livia. Female urine- 

 genital organs, cl.2, urodaeum ; cl.j, proc- 

 todaeum ; k. kidney ; /. od. left oviduct ; 

 I od' . its cloacal aperture; l.od". its 

 coelomic funnel ; /. od'" . its ccelomic aper- 

 ture ; ov. ovary ; r. od. right oviduct ; 

 y. od '. its cloacal aperture ; ur. ureter ; 

 ur'. its cloacal aperture. (From Parker's 

 Zootomy.) 



and is fed by the parents with a secretion from the crop, the 

 so-called " Pigeon's milk." 



Of recent Birds two main divisions are recognised 

 the Ratitae and the Carinatae the former comprising only 

 the Emus (Dromaus) Cassowaries (Casuarms) and Kiwis 



