ULTIMOBRANCHIAL BODY, FIFTH POUCH-BIRDS 585 



lum was interpreted by Rabl to represent a true sixth visceral 

 pouch in birds. 



My own observations ('17) have shown that two diverticula 

 corresponding to those in the duck are developed in the pied- 

 billed grebe. It is the purpose of the present paper to report the 

 development of two such evaginations also in species representing 

 two additional families of wild birds and in the chick. 



Coot and gallinule. These two species present practically iden- 

 tical conditions. They show particularly well the relations of 

 the fifth pouch and the ultimobranchial diverticulum in birds. 

 Figure 3 represents the structures in this region of a gallinule 

 (Gallinula galeata galeata Licht.) of approximately four and 

 one-half days. The fourth pouch has a relatively long dorso- 

 ventral axis. The fifth pouch forms a narrower parallel diver- 

 ticulum which is about three-fourths as long dorsoventrally as the 

 fourth, is directed slightly more caudally, and at no point touches 

 the ectoderm. The two pouches are at the end of a rather elon- 

 gate common diverticulum of the pharynx which, because of an 

 approximation of the two pouches in width, has the appearance 

 in sections of being divided distally into twin lobes, very similar 

 to the condition in the duck as described by Rabl. The fifth 

 pouch of the left side is distinctly longer and broader than that 

 of the right. The fifth aortic arches are complete. That of the 

 left side lies in the angle between the fourth and the fifth pouch, 

 i.e., in the fifth visceral arch, but the one on the right courses 

 along the lateral border of the fifth pouch. The ultimobranchial 

 diverticulum is just beginning to appear on the left side of the body 

 as a slight bulging of the common pharyngeal diverticulum, 

 medial to the fifth pouch. 



Figure 5 represents the parts concerned in a coot (Fulica 

 americana Gmel.) of about six days. The fifth pouch, though 

 still conspicuous, is much reduced as compared with that of the 

 four and one-half-day gallinule. The fifth aortic arch has in 

 greater part disappeared, its dorsal end alone persisting as a 

 short branch of the sixth. On the right side the diverticulum of 

 the ultimobranchial body is not yet discernible, but on the left 



THE JOURNAL OF MORPHOLOGY, VOL. 31, NO. 3 



