1895.] LXTNGS OP SKAKBS, A.lIPHISB.i;NrDJE, ETC. 697 



lung, the embryological evidence, judging by the forms I have been 

 able to study, is not so clear, because I have found no trace of 

 more than one lung from the first. Thus in Vipera aspis and 

 Typhlops lumhricalis I have stages which show the lung from an 

 early stage inclining to the righ* side, after the manner of the 

 right lung in the corresponding stages of such a form as Tropido- 

 notus nah^uv, but there is no trace of a left lung. 



In the case of many morphological questions, it is considered 

 sufficient to study the development of a single typical species. 

 But in the present case this is not so ; for my gainsayers represent 

 that in some iSnakes one lung is developed, and in some the other. 

 Now embryological evidence is of course the most convincing, but 

 it is manifestly hopeless to think of studying the development of 

 the lungs of every species of iSnake, and, in the absence of embryo- 

 logical evidence, that of comparative anatomy is quite cogent 

 enough I think for our present purpose. I therefore propose to 

 show how we may easily tell the right lung from the left in any 

 growTi Snake by the light of comparative anatomy. 



In most pulmouate vertebrates there can of course be no doubt 

 as to which is the right and which the left lung, for the two lungs 

 hang in separate lateral portions of the body-cavity, separated from 

 each other by one or, more usually, by two membranous septa. 

 There can be no question about the matter in the case of Amphis- 

 bsenians and other Lizards, and any discordant statements about 

 the lungs of these animals must be simply the result of a mistake, 

 whether on the part of the observer, the compiler, or the printer. 



With Snakes, however, it is otherwise. In Snakes as we know ^ 



the body-cavity is in its anterior region obliterated except for the 



pericardium and the two sacs which encase the right and left 



halves of the liver ; and moreover the viscera show a displacement 



of a more or less rotatory character. It thus happens that though, 



in the great majority of cases, the rudimentary lung, if present, 



will be found just where, after seeing the rudimentary lungs of 



snake-like hzards and of Gymnophiona, and also on embryological 



grounds, we should expect to find the rudiment of the left lung 



of a Snake — [viz. on the left posterior border of the heart] — still 



there are a few species, e. g. Heterodon platyrhinus [see (7) pi. xv. 



or (8) pi. xxviii., and figs. 1-4 of this paper], in which first 



appearances are somewhat deceptive, so far as the rudimentary 



lung is concerned. In hke manner, though the larger, more 



dorsally situated lung which Cope speaks of as the "left laug" 



has in most cases, to myself personally, appeared pretty clearly to 



be the right lung, still in many cases the position of this lung is 



so far median, or partly inclining to the right and partly to the 



left side of the animal, that an observer whose studies had not 



led him to investigate closely the relations of the organs in these 



animals might be in doubt. Tet once looked at the right way, the 



lungs of Snakes present hardly more difficulty than the lungs of 



Lizards and Amphibians. 



1 Cf. Pioc. Zool. Soc. 1892, pp. 477-498. 



