146 DISCOVERY REPORTS 



The lung is now well developed with numerous passages radiating from the ecto- 

 bronchi and entobronchi. These are the first of the parabronchi (Fig. i d, pb). Besides 

 the rudiments of the posterior thoracic and abdominal air sacs, the lungs bear the pro- 

 cesses which afterwards develop into the other three air sacs of the hatched bird — 

 cervical, interclavicular, and anterior thoracic. In addition to these permanent air sacs, 

 the lung buds out five other papillae on the dorsal surface at this stage, which do not 

 persist (Fig. i e, do). 



It has long been known that the lungs of certain of the Reptilia expand into air 

 sacs. They are very much smaller in the chameleon for example than they are in modern 

 birds, but they are also more numerous (Heilmann, 1926, p. 128). It is probable there- 

 fore that the additional outgrowths on the dorsal surface of the lung at this stage 

 represent a more primitive condition. 



Limb buds. Fore-limb elongating with extraordinary rapidity. The contour and cha- 

 racter of the future flipper is plainly seen. The hind-limb is digitate with webbing 

 between the toes. 



Feathers. The first rudiments of feathers make their appearance as papillae growing 

 in the skin of the tail region. The tongue (/) is visible intra-orally. 



7. Stage comparable with a fowl of about 13 days' incubation (Plate IV, fig. i). It is 

 beyond the stages included in the Normentofel, and for convenience it is assigned here 

 to stage 37. Length 85 mm., including beak. Eye protected by well-developed lids. 



Feather rudiments distributed all over the body. They appear last on the fore-limbs, 

 and the rudiments in this situation grow into feathers exactly like those that develop on 

 other parts of the body. There is no reason to suppose, therefore, that they have ever 

 previously been modified for the purposes of flight. In the water, indeed, the fore- 

 limb is used entirely as a swimming organ and it seems reasonable to regard it as 

 a flipper rather than as a wing. Its length at this stage of development in relation 

 to the rest of the body is quite out of the ordinary (Plate V, fig. 2). The hind-limb 

 is also disproportionately large. Webbing extends nearly to the ends of the digits and the 

 latter are thoroughly protected at their tips by thick cushions of integument ("neo- 

 nychia" — Agar, 1909, p. 374), which prevent the possibility of damage to the amnion 

 or other delicate membranes. 



Viscera. These are illustrated by dissections (Plate IV, fig. 2 and Plate V, fig. i). 

 A few points call for comment : 



(i) The alimentary canal. The crop region {cr) is not really separate from the stomach. 

 It is a characteristic of penguins that the whole of the anterior division of the canal is a 

 continuum which is enormously distensible (Wilson, 1907, p. 43). The capacity of the 

 fledglings for food, and the necessity the adults are under of landing sufficient for their 

 own needs as well as for the voracious young are well known facts (Wilson, 1907, p. 44 ; 

 Levick, 1910, p. 80, etc.). It is not surprising therefore to find, quite early in develop- 

 ment, that the anterior part of the alimentary canal is exceptionally wide. 



(ii) The vascular system. The heart and main blood vessels are typically avian. In 



