412 



THE EYP] IN EVOLUTION 



^wSi^ 



mm 



Fig. 509. — The Pleated Type of Pecten. 



(A) vertical longitudinal section ; (B) transverse horizontal section ; (C) and 

 (D) transverse vertical sections (Thomson). 



perching (passerine) birds, 30 in the jay, Garrulus ; in predators the folds are 

 thicker but fewer (13 to 17). Sea-birds and shore-birds tend to have fewer pleats, 

 usually less than 12 ; Anseriformes (ducks and geese) average between 10 and 

 16 ; while the terrestrial Australian goose, Cereopsis, has only 6. Nocturnal 

 sea-birds have very few (7 in the stone -cvirlew, (Edicnenms). Other nocturnal 

 forms have a similarly simple structure ; the swift, Micropus, has 11 pleats, the 

 owl. Bubo, 5 to 8, and its relatives the European night-jar, Caprimulgus, 3 to 5, 

 and the frog-mouth, Podargus, 3 to 4 ; none of these three members of the owl 



Fig. Ti! ';,— The Simple Pleated Pec- 

 ten .; THE Barn Owl, Stbix 

 FLAM (Casev Wood). 



Fig. 511. — The Elaborate Pleated 

 Pecten of the Red -headed 

 Woodpecker, Melanerpes ery- 

 throcephalus. 



