320 



Proceedings of the Royal Physical Society. 



In the Dipnoi the lungs are connected mid-ventrally with 

 the gut in Lepidosiren and Protopterics, ventro-laterally in 

 the case of Gcratodus. But in none of these has the develop- 

 ment been investigated. It seemed important to me to see 

 if in the group supposed to connect fish and amphibian there 

 was anything to connect the swim-bladder of the one with 

 the lung of the other. The answer is in the negative. The 

 lung of Ceratodus arises like the lung of amphibians, so that 

 the resemblance of Dipnoi to Amphibia is emphasised, and 

 their remoteness from the Teleostomi. 



In a young Ceratodus of about 14 mm. in length, and 

 labelled "two months after hatching," I found a very early 

 stage in the development of the lung. But in smaller 

 specimens of less age I have distinctly later stages in the 

 growth of the lung, so stress cannot be laid on size and age. 



In my first stage, the foundation is only about ^io ^^- i^ 

 length. It consists of a slight ventral pit or depression in 

 the floor of the phai:ynx about the same level as the first 

 pronephric nephrostome, and just posterior to the heart. It 

 is quite median in position, and so differs from the com- 

 munication between lung and gut in the adult. (See Fig. 1.) 



Fig. 1. C = C(jeloin ; Ch. =notochord ; 

 G = gut ; L = foundation of lung ; 

 N = pronephric nephrostome; P 

 = pronephros. 



Fig. 2. A = aorta; D := diverticulum 

 of ccelom ; Gl. = glomerulus ; 

 other letters as in Fig. 1. 



