STAGES OF DEVELOPMENT 



145 



Brain. Rapid growth of the hemispheres and the commencement of the growth of the 

 cerebellum combine to change the contour of the head to a dome-like shape. 



Eye. The wall of the sclera bears a number of papillae strongly recalling the sclerotic 

 ossicles so commonly seen in the fossils of extinct aquatic reptiles and present in the 

 sclera of many birds. In the penguin their incidence is apparently only of short duration 

 at this stage in development. When the eyelids have grown they disappear (of. papillae 

 conjunctiva sclerae in the fowl, Lillie, 1908, p. 280). 



•mb 



'--.v.icl 



DtK 



Fig. I. The lung and air sacs, a, stage 25 ; b, stage 31 ; c, stage 37; d, stage 34. a, b, r, and d, diagrams of 

 the right lung drawn from the right side; e, the same lung as d, dorsal view. 



ab, abdominal air sac ; «?//, anterior thoracic air sac ; ce, cervical air sac ; do, dorsal papilla ; ecb, ectobronchus ; 

 enb, entobronchus ; id, interclavicular air sac; mb, mesobronchus ; pa, pulmonary arterj^; pb, parabronchus ; 

 pth, posterior thoracic air sac; st, systemic artery. 



The external auditory meatus takes on the adult appearance. 



All traces of the visceral openings on the neck have vanished. The intestine is thrown 

 into two spirals completely enveloping the rudiments of the pancreas. The spleen de- 

 velops on the omphalo-mesenteric artery. 



