REPORT ON THE ANATOMY OF THE PETRELS. 37' 



Aeipetes antarcticus (figs. 20, 21), commonly placed in the genus Thalassceca with 



Fig. 17. 



-Syrinx of Ossifraga gigantea, 

 from before. 



Fig. 18.— The same, 

 from behind. 



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Fig. 1 9. — 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 paral- 

 lel tubes, through the left of which a 

 pointer is passed, below, and terminating 

 above by a free margin. 



Thalassceca glacialoides, completely differs in the structure of its syrinx from the last 

 three species described, and is more like Prion. The two first pairs of bronchial rings 



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Fig. 20. — Syrinx of Acipctcs antarcticus, from before. 



Fig. 21. — The same, from behind. The smaller figure 

 represents a section of the trachea, to show the 

 imperfect septum dividing it. 



are complete anteriorly, the second being ossified, for a small extent only, in the middle 



