1895.] LUNGS OF SKAKES, AMPHISBJENIDJE, ETC. 709 



carried a step farther and that the ancestors of this second, like 

 those of the first, had some trace of a second lung. 



Secondly, what significance may we attach to the suppression of 

 one or other lung ? Can we, I mean, correlate such suppression with 

 any other anatomical or physiological characters ? 



As we know, there is, as a rule, on the whole a very distinct bilateral 

 sjTnmetry in the bodies of pulmonate vertebrates, but there is also, 

 as is well known, one marked departure from such symmetry which 

 appears early, with which may, I think, be correlated certain 

 departures from symmetry in some of the other organs. I refer 

 to the marked leaning of the stomach to the left side. "Whatever 

 be the cause of this, we have the fact, as also the fact that in the 

 case of these abnormal specimens in which the position of the 

 stomach is reversed there is wont to be a reversed position of the 

 great vascular trunks (the aortic root and the postcaval vein) and 

 other correlated changes. There is, then, evidently a correlation 

 between the asymmetry of the stomach and the asymmetry of 

 some of the other organs ; and while in some cases it may be better 

 to say that both are due to some common cause, in other cases 

 (and I think this difference in the size of the lungs one of them) 

 it would seem reasonable to speak of the asymmetry of the 

 stomach as a cause of the asymmetry in the other organ. 



From the fact, however, that only some of the animals which 

 have the asymmetrical stomach have unequal lungs, it is obviously 

 not by itself a sufficient cause. The leftward inclination of the 

 stomach and adjoining part of the oesophagus only leads to inequahty 

 of the lungs w^hen some second cause, such as the snake-like 

 habit of the body [which naturally renders the accommodation of the 

 viscera a work of greater difficulty], or in mammals some other 

 cause [which I will presently suggest], is superadded. 



This view harmonizes with the fact that in the Amphisbsenidae 

 [in which the left lung is the larger] the leftward displacement of 

 the stomach is but small, while the oesophagus is sometimes markedly 

 displaced to the right side. Of course this, as it stands, might 

 suggest that we had here merely a case of mechanical displacement 

 of the oesophagus and stomach by the left lung instead of an 

 obhteration of the right lung by the rightwardly inclined alimen- 

 tary canal. But in certain of the Amphisbaenidae [e.g. AmpJiisbcena 

 alba and Anops Jcingii, two forms with a total absence of right 

 lung] it is clear that we have something more than this, for though we 

 have no case of "situs inversus " of the postcaval vein, which runs as 

 usual on the right side, we find that the veins from the stomach to 

 the liver are not as usual confined to the median gastro-hepatic 

 ligament, but run in that right dorsal hgament of the liver (the 

 " Hohlvenengekrdse " mentioned above, p. 698) which usually 

 carries none but systemic veins, such as the postcaval and vertebro- 

 intercostals. It is at least interesting that this, so far as I am aware 

 unique, feature of the vascular system, which, I take it, argues 

 that the stomach is morphologically more to the right side than 



