406 



ON THE PETRELS COLLECTED DURING 



syrinx of Bulweria macgillivrayi. In this specimen * the rings are 

 asymmetrical there being only three, instead of four, bronchial rings 

 between the pessular ring and that which bears the muscle on the left 

 side, apparently owing to the suppression of the second bronchial ring, as 



Zool. Chall. 

 Exp. vol. iv. 

 pt. xi. p. 37. 



Fig. 19. 





CD 

 00 



oo 



a, b, c, sections of syrinx and trachea of Ossifraga along the lines a, b, c, of fig. 17, to 

 show the double nature of the tracheal tube below, and its complete division by a 

 median septum above ; d, trachea opened from the side, to show the median 

 septum, dividing it into two parallel tubes, through the left of which a pointer 

 is passed, below, and terminating above by a free margin. 



Ibid. p. 38. may be seen in the figures (figs. 22, 23, p. 408) and irregularly developed, 

 tending thus to hide the typical form. The last three tracheal rings are, 

 anteriorly, more or less united, there being a pessular bar developed on 

 the inferior margin of the last ring. Posteriorly, the antepenultimate 

 of these is quite free and complete ; the next is incomplete posteriorly, 

 whilst the last is complete on the right side, but anchyloses on the left 

 with the first bronchial laterally. The third bronchial rings on each 

 side are complete, thus encircling the bronchi. The fourth is free and 

 incomplete. 



Puffinus (as represented by Puffinus brevicauda) presents a simple form 



* Some of the peculiarities here described may be due to its being a youngish bird. 

 I have, unfortunately, as yet been unable to examine the syrinx of Bulweria columbina, 

 which might throw some additional light on the subject of the affinities of this 

 genus. 



