708 ME. GEEARD W, BTJTLEE ON THE [NoV. 19, 



The first two questions are very interesting, and I hope shortly 

 to return to their discussion in another paper. For the present 1 

 may merely say that I incline to a view similar to that suggested 

 hy Goette in 1875, namely that the lungs have arisen from paired 

 lateral branchial pouches \ 



Anyone who adopts this view will recognize a certain tendency 

 to pairedness of the lungs as primitive. It seems, however, highly 

 probable that lungs have arisen [from some such common anlage] in- 

 dependently in the different groups of vertebrates, and that we ought 

 not to conclude that all pulmonate vertebrates are descended from 

 a common pulmonate ancestor. To find such common ancestor we 

 should perhaps have to go back to a time long before the first 

 appearance of pulmonary respiration. It is thus quite con- 

 ceivable, even accepting Goette's view, that in the ancestors of 

 certain one-lunged types the branchial pouch of one side may have 

 from the first remained rudimentary, that of the other side alone 

 developing into a lung. Such a view is also quite in harmony 

 with embryology ; for in the embryos of such forms as Vipera 

 aspis and Typlilops lumbrimlis there is no trace of a second lung 

 even in early stages. "While, however, neither embryology nor the 

 theory of homology with paired branchial pouches runs counter 

 to the view that the ancestors of some pulmonates may from the 

 first have had but one lung, while others had two, it seems to me 

 that there are certain facts of comparative anatomy which are in 

 favour of the view that in their first beginning the lungs were not 

 only potentially but actually paired in the ancestors of many species 

 which now have no trace of more than one. 



Thus, as is well known, we find cases of two species of Snake 

 which are so alike in other respects as to be classed in the same 

 genus, one of which has a rudiment of the left lung, while the other 

 has no trace of such ^. Now the pesistence of the rudiment as such 

 a definite structure in the adult, combined with the fact that the 

 rudiment is of pi'oportionally greater size in the embryo, suggest 

 that it is the reduced remains of an organ which was once a 

 functional hmg. If, then, a functional lung can be reduced to 

 a mere functionless rudiment, it seems likely, when we find two 

 species of the same genus, one of which has such rudiment while 

 the second has not, that in this second the reduction has but been 



^ The clue to my reason for taking this view is briefly this, that I find that 

 in the Lizard, Snake, and Bird the oesophagus becomes separated ofl', from 

 behind forwards, from the anlage of the lungs and from the trachea, just as it 

 ■would appear from Kestler's observations the anlage of the oesophagus is sepa- 

 rated off from the branchial chamber in the metamorphosis of Ammocceies into 

 Petromyzon [Nestler, 'Archiv fiir Naturgeschichte,' Jahrg. Ivi. Bd. i. pp. 100- 

 106]. From the best published accounts the same is true of the development 

 of the oesophagus, lungs, and trachea of Amphibia and Mammalia. 



^ Thus in my list above Crotahts horridus has a small rudiment, while 

 C. di/rissiis has none ; Ji/cqjs hygeia has a rudiment, while E. fidvius has none. 

 Similarly, in Cope's paper (7) p. 223, we have such a difference recorded in two 

 other genera besides Crotalus, viz. in Bothrops and Ancistrodon. 



