1906.] ANATOMY OF THE OPHIDIA. 43 



however, being rather anatomical than physiological, this mode of 

 compensation — as it maybe considered to be — will be left aside. 

 For it is, I think, impossible to hold, in the present state of our 

 knowledge at any rate, that the unpaired condition of the lung is 

 the primitive one for Snakes, and that the minute rudiment of the 

 second lung in many Vipers and Colubrines is an incipium of a 

 second lung. Still the question does not appear to me to be 

 absolutely settled, for reasons which I hope to investigate more 

 fully later. 



But although it may be said that there is some evidence that 

 among the Ophidia the existence of a tracheal lung is not an 

 innovation but an inheritance, the case would seem at first sight 

 to be quite different among the Lacertilia. If the assumption 

 that the Lacertilia form one order with the Ophidia,, and the 

 theory which I seek to prove concerning the origin of the lungs 

 in the Squamata be probable, there should be evidence of a 

 positive kind among the Lacertilia of the existence of traces of a 

 tracheal lung. The most positive piece of evidence is that furnished 

 by Prof, Wiedersheim, who has described in Amphislxena faUginosa 

 what appears to be a persistent tracheal lung "*, the existence of 

 which, however, has not been confirmed for other species t. It is 

 noteworthy, too, that in various Lizards the tracheal rings are far 

 from meeting posteriorly ; in Lacerta, for instance, there is a very 

 wide membranous interval posteiiorly, at the edge of which only 

 appear the tips of the tracheal rings. Furthermore, in many 

 Lizards — this is particularly well seen in Varanus — the lung ex- 

 tends forward a good way beyond the entrance of the bronchi into 

 the lung. The arrangement in such a lizard as Varanus is quite 

 reminiscent of the disposition of that organ to be seen in Heterodon 

 platyrrhinos, where the tracheal lung is not traversed by a tracheal 

 gutter, but extends forward along the intact trachea as a con- 

 tinuation forwards of the thoracic lung. 



Were it not for the numerous cases of a tracheal lung attached 

 to the trachea throughout, this condition in Heterodon would 

 probably have been compared merely with the slight forward 

 extension of the lung in many Lacertilians, in which the bronchus 

 enters at the side rather than at the base of the lung. Such a 

 comparison w^ould indeed be correct, but it would not be so far- 

 reaching as I believe there are grounds for regarding it j. Besides, 

 this incomplete comparison of facts, as I regard it, would leave it 

 an open question as to whether the lungs in the Squamata were 

 not derivable from the type shown in Hatteria, and to which a 

 forward extension had been afterwards added. As it is, there 

 are further facts which enforce the position taken up by me 

 in this communication. I have pointed out, in describing the 



* ' Lelii'buch der vergleichenden Anatomie der Wirbelthiere.' 



t Beddard on AmpMshcena, P. Z.S. 1905, vol. ii. p. 489. 



X This statement of course assumes the validity of Prof. Cope's view that the 

 headward extension of the lung in Heterodon is the homologue of the tracheal lung 

 in, e. g., the Viperidse. 



