430 STRUCTURE AND CLASSIFICATION OF BIRDS 



four in A rdetta and Botau nt*. The number of rectrices differs 

 much ; there are only eight in Ardetta exilis and A. involucris, 

 ten in Botaiirus (not invariably), twelve in Ardea cocoi and 

 ( 'tuicroma cochlearia. 



The ptenjlosis differs from that of the storks by the 

 narrowness of the tracts. The spinal space begins with the 

 commencement of the neck, and only terminates a little way 

 in front of the tufted oil gland. The anterior part of the 

 spinal tract is not always more strongly feathered than the 

 posterior part, and there is (according to the figures of 

 NITZSCH) hardly a break between them. The ventral tracts 

 also are separate early on the neck. In Cancroma they divide 

 on the breast into a broader, stronger outer tract, which ceases 

 just below the metapatagium, and a narrow inner tract. The 

 anterior ventral powder-down patches constantly interrupt 

 the continuity of the anterior and posterior sections of the 

 ventral tracts. 



A curious absence of any apparent relationship between 

 the relative length of the sections of the alimentary canal, 

 and of the alimentary canal as a whole, and of the food, is 

 shown by the above table, drawn up by Mr. GAEBOD, 

 which I reproduce here from his notes. 



They seem, however, to ally the last four genera, which 



