170 EMBEYOLOGY OF THE LOWER VERTEBRATES CH. 



twists upon itself, in such a way that points upon its ventral surface 

 would move towards the eiiihryn's right side. (In other words the 

 lung -rudiment rotates about its long axis in a counter-clockwise 

 direction as seen from behind, its front end remaining fixed.) The 

 two lobes are the right and the left lung-rudiment but on account of 

 the rotation just mentioned which extends through more than 180 

 the left lobe at this stagr represents what was originally the right 

 side of the rudiment. 



The two lungs of Lepidosiren or Protopterus are thus reversed in 



FIG. 96. Dissections of mid-gut of Lepidosiren at stages 32 (A), 35 (B), 36 (C), and 

 37 (D), showing the modelling of the intestine and also the later stages in the 

 development of the lungs. S-cii from the dorsal side. 



c.c, cloacal caecum ; int, intestiiif ; /./, IH't Inn/,: //, li\cr; /// ;<.</. Wulftian duet ; ]>n, p;mr: 

 I'h. pharynx; /./. ri-lit liiii^ ; /', splc.-n. 



position the right lung of these I mi us l.rin^ homologous with tl it- 

 left of other Vertebrates. An important detail is that in early stages 

 tin- original right lung, i.e. the definitive left, is decidedly larger than 

 its fellow (\''\x. 95, B). In later stages this ine([ualitv <lisa|jiears, the 

 smaller lunjj <.\ei taking the other in its -routh ( Fig. 96). 



In the case nf nmst individuals the In iinie tlieir dorsal 



[>o8ition .simply hy ^i'd\\in- directly tail wards, the oesoplia^ns heinu 



pushed (nil nf the \\ay |u\\ards the left side (Graham Kerr. I'.'Ki . 



ilain sjii which doubtless in this respect retain 





