1906.] EESPIRATORY SYSTEMS IN THE OPHIDIA, 529 



additional evidence for the position which I ventured to take up 

 in a recent communication to the Society*. I there expressed the 

 view that the tracheal lung typically exists in the Ophidia, and 

 that those cases where no traces are to be found are to be looked 

 upon as a reduction from a former state of affairs where the 

 tracheal lung was fully developed and functional. It seem 

 unlikely that the reverse is the case, and that the various genera 

 in which undoubted remains of a tracheal lung are now to be 

 found have independently acquired that structure. If such 

 instances were limited in number to a very few, that view might 

 with greater reason be adopted. As it is, it appears, from wha,t 

 we know of compai-ative anatomy, to be not at all likely that a 

 complex series of modifications, resulting in the change of 

 structure and vascularisation of a membrane uniting the separate 

 edges of the tracheal semirings, should independently and so con- 

 stantly occur as the facts would then demand. 



The new instances which I have been able to bring forward in 

 the present communication thus furnish additional arguments for 

 the correctness of my way of looking upon the matter, as I think. 

 It is interesting to note the v/ays in which the tracheal lung has 

 disappeared. In two Snakes so remote in the system as are 

 Coluber corals and Sepedon hcemachxites we have a practically 

 irlentical disposition of the lung. In both, the precardiac portion 

 of the lung is a very wide sac along which the trachea runs as a 

 gutter, and at the lowest extreme of which only is there any 

 development of lung-tissue. There is no question here of a 

 tracheal sac sepa,rate from the ensuing lung. Both organs are 

 evidently continuous. Nor is there a fixed line of demarcation 

 between the two regions ; the one fades into the other. On the 

 hypothesis of a reduction, the sti-ucture of both of these genera 

 can be derived from such a condition as is preserved in the 

 Viperidfe ; or, if the introduction of a family, generally regarded 

 as much modified, be objected to (though it does not follow that 

 the Yipers are not archaic in one particular structure), then the 

 Bold Ungalia may be adduced, so far as I can judge from 

 Prof. Cope's statements. 



In Coluber longissimus and Erythrolamprus cesculapii, two 

 Snakes equally as remote from each other as are the two examples 

 just treated of, the modification is evidently taking place along 

 slightly different lines. In these Serpents the lung has apparently 

 shrunk in diameter before commencing to atrophy as a lung, but 

 the process of lung disappearance has taken place from before 

 backwards. The initial stage of this series of modifications is 

 ofiered by such a type as Ghersydrus granulatus, in which the 

 tracheal lung, according to Cope's figure t, is of considerably less 

 calibre than the tracheal lung of a Yiper, These are the two 

 principal lines along which the degeneration of the tracheal lung 

 has taken place: i. e., firstly the disappearance of the lung-tissue, 



* " Contributions to the Anatomy of the Opliidia," P. Z. S. 1906, vol. i. p. 41. 

 f Loc. cit. pi. xiii. 



36* 



