Description of tlie Modilications of certain Organs. 645 



Fig. 25 shüws tliese orgaus in situ in an advanced embryo of the 

 English sniall Petiel, collected by Prof. Newton at St. Kilda. Fig. 26 

 shows the same in the adult. The reversion is alrcady repeated in 

 the young bird, although the uecklike connexion betvveen gizzard and 

 proventricular sac is still less inarked, and the rotatiou of the duo- 

 denal portion is less advanced. 



The mechanical causes of this reversion of the stomach are siniilar 

 to those of the Ostrich. The place of the gravel is taken by Cepha- 

 lopods and other marine animals, swallowed wholesale by the Tubinares, 

 as is indicated by the wide cropless gullet and by the frequent occur- 

 rence of the chitinous beaks of Cephalopods in this proventricular sac. 



Description of the Plates. 



Fig. 1 e '2. The beaks of two right-billed males of the Crossbill, Loxia 



curvirostris; nat. size. 

 Fig. 3. Beak of a right-billed male of the Parrot-Crossbill, L. pityo- 



psittacus; nat. size. 

 Fig. 4. Beak of a nestling of L. curvirostris; nat. size. 

 Fig. 5 a 6. Dorsal view of the bills of an adult and a very young 



specimen of the Wry billed Plover, Anarhynclms frontalis ; nat. size. 



Fig. 7. Transverse diagramatic section through the trachea and pouch 



^ of an adult Dromaeus ; reduced, from a specimen in the Cambridge 



^ Museum. 



Fig. 8. Ventral view of the trachea and pouch of an immature male 



of Dromaeus; i'educed; after Mukie. 

 Fig. 9. Ventral \aew of the trachea of a very young chick of Dro- 

 maeus ; nat. size. 

 Fig. 10. Sagittal section through head and laryngeal apparatus, with 



reference to the position of the trachea to the manubrium sterni, 



of an adult Mycetes sp. nat. size, from a specimen in the Cambridge 



Museum. 

 Fig. 11, 12, 13. The manubrium sterni of varioüs species of adult 



Mycetes, after Parkee, Mivart and Albkkcht. The manubx'ial parts 



are toned grey. 

 Fig. 14. Outlines of an Ostrich, with the position, size and shape of 



the stomach drawn in. 

 Fig. 15. Shape and position of the stomach of a nearly adult Ostrich, 



when nearly empty. ^/j. nat. size. 



Zool. Jahrb. V. Abth. f. Syst. 42 



