THE VOYAGE OF THE 'CHALLENGER.' 



401 



the first and fourth bronchial rings are free, whilst on one side the 

 second and third are quite fused both before and behind. The last 

 tracheal ring is free throughout. 



Fig. 9. 



Zool. Chall. 

 Exp. vol. iv. 

 pt. xi. p. 34. 



Syrinx of Cymochorea leucorrkoa, from before. 

 Fig. 10 



The same, from behind. 



Daption much resembles Payodroma, there being a bony box, formed Ibid, p. 35. 

 however by the fusion of the first three bronchials with the last tracheal 

 ring. In neither of these genera is there any trace of a tracheal 

 septum . 



It is by a further development of the syrinx of Pagodroma that the 

 peculiar one of the Fulmars is formed. 



In Thalassceca ylacialoides (figs. 15, 16, p. 404) the last two tracheal rings 

 are ossified andfused together anteriorly, amedian descending process being 

 developed which lies between the similarly ossified and fused first three Ibid. p. 36. 

 bronchial rings. The fourth pair of rings is also ossified, but free from 

 those that precede it, at least anteriorly. Posteriorly the first four bron- 

 chial and last four tracheal rings are firmly co-ossified into a large 

 pessular box, whilst ossification in the median line (both before and 

 behind) of a number of the cartilaginous tracheal rings above this forms 

 the line of attachment for the median septum which divides the tracheal 

 tube for an extent of about 1-25 inch. 



2D 



