636 



Dr. HANS GADOW, 



We have here an instance of the inheritance of an organ by the 

 embryos of both sexes, which in the adult persists only in the male. 

 We cannot well assume that the ancestral Anatinae were possessed 

 of such swelliugs in both sexes, although they are now almost uni- 

 versal in this group of birds. These swellings are, without exception, 

 restricted to the males ; they occur on both sides, or on one side only, 

 and in the former case the swelling on the left side is generally the 

 larger. 



4. The tracheal pouch of the Emn. 



The adult Emus of both sexes possess a large pouch on the ven- 

 tral side of the trachea; its lumen communicates with that of the 

 trachea through a longitudinal slit which is produced by a variable 

 number of the cartilaginous tracheal rings being deficient in the medio- 

 ventral line. The total, and also the serial, number of these split 

 rings varies individually, as the following table will show, within 

 considerably wide liraits. As many as 14 and as few as 5 rings are 

 known to be thus afifected, Their position is at about the beginning 

 of the lower third or fourth of the whole trachea. 



52 

 53 

 54 

 55 



56 

 57 

 58 

 59 

 60 

 61 

 62 

 63 

 64 

 65 

 66 







The deficient tracheal rings are rounded off and stand asunder 

 to the extent of 0,5—1,0 cm. The tracheal pouch is lined with the 

 same mucosa as the inside of the trachea itself, and its lining passes 



