THE VOYAGE OF THE * CHALLENGER. 



403 



those of opposite sides being quite separate, whilst above, by the gradual 

 diminution of their opposed interior halves, they become, when viewed 



Fig. 13. 



Zool. Chall. 

 Exp. vcl. iv. 

 pt. xi. p. 35. 



Syrinx of Pagodroma nivea, from before. 

 Fig. 14. 



The same, from behind. 



from outside, simple rings of the normal tracheal type. On section, jbid 36 

 however, it is seen that their ends are still incurved to form a tracheal 

 septum like that of Fulmarus and Thalassceca. This completely divides 

 the trachea into two tubes for a space of about 3| inches, terminating 

 above by a free semi-lunar border, concave upwards (fig. 19, c, cZ, p. 406). 

 In fig. 19 three sections are given of the inferior portion of the trachea 

 made along the lines a, 6, c, in fig. 17 (p. 405), to show how the two 

 tracheal tubes, separate below, gradually unite above. 



2D2 



