38 



THE VOYAGE OF H.M.S. CHALLENGER. 



line. The lowest tracheal ring is quite simple anteriorly, and posteriorly it sends forwards 

 a pessuliform process, anchylosed in front with the second bronchial rings. Two pairs 

 of the bronchial semi-rings (3, 4) are ossified at their posterior extremities, but not fused 

 in any way. The penultimate tracheal and preceding rings are, as in Fulmarus, &c, 

 ossified posteriorly in their median (narrowest) portion only to bear the tracheal septum. 

 This, however, is not {vide fig. 18, a) a complete septum, but is incomplete, the incurved 

 posterior ends of the rings not reaching the anterior wall of the trachea by some little 

 way. Its vertical extent is small, ceasing about "85 inch above the bronchi. 



The peculiar genus Bulweria is, perhaps, as far as regards tracheal structure, nearer 

 the small Storm-Petrels (Procellaria and Cymochorea) than any other group, judging at 

 least from my examination of the syrinx of Bulweria macgillivrayi. In this specimen 1 

 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 may be seen in the figures (figs. 

 22, 23), — and irregularly developed, tending thus to hide the typical form. The last 



Fig. 22. — Syrinx of Bulweria macgillivrayi, from before. 



Fiq. 23. — The same, from behind. 



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 ante-penultimate 

 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 of syrinx 

 (figs. 24, 25), the two first bronchial rings being complete anteriorly, the succeeding 

 two being only semi-rings. The two last tracheal are united with the two first 

 bronchial behind, sending off a pessular process, which anteriorly, as usual, is continuous 

 with the third semi-rings. In younger birds (fig. 26) the various rings concerned 

 remain more distinct, the pessular bar, it is pretty clear, being largely formed by the third 



1 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 colurnbina, which might throw some additional light on the subject of 

 the affiidties of this genus. 



