584 CHARLES EUGENE JOHNSON 



ron's ('86) statement that this fifth pouch becomes detached 

 from the pharynx and also from the fourth pouch in embryos of 

 six days, but remarks that in his own material he did not observe 

 the separation from the fourth pouch, although he examined a 

 number of embryos of that age. 



Mall ('87) derived the ultimobranchial body ('corpus y') from 

 what was called by him the 'fossa subbranchialis' and which from 

 his description differs in no way from the fifth pouch of Kast- 

 schenko and other authors. Mall mentions this fossa subbran- 

 chialis first, and illustrates it clearly, in the description of the 

 visceral pouches of an embryo of three days, seven hours. 



Liessner ('88) recognized the fifth pouch in embryos of 84 

 hours. At 120 hours, he states, the fifth pouches reach their 

 maximum development and at 126 hours they have completely 

 disappeared. The ultimobranchial body is not mentioned by 

 Liessner, and the meaning of his statement that the fifth pouches 

 disappear is not clear. 



In none of the accounts of the development of the visceral 

 pouches and the ultimobranchial body in the chick is there any 

 reference to more than one diverticulum associated with the 

 fourth visceral pouch, and all authors, with the exception of 

 Mall, who describes the 'fossa subbranchialis' as an outpouching 

 from the ventral aboral region of the fourth pouch, call this 

 diverticulum the fifth visceral pouch. 



In the duck and the house-sparrow (Passer domesticus) Kal- 

 lius ('05) demonstrated the presence of a well-developed fifth 

 visceral pouch, but the ultimobranchial body is not discussed 

 by this author. On the other hand, Helgessen ('13) for the 

 house-sparrow and Hamilton ('13) for the duck make no men- 

 tion of a fifth visceral pouch, but derive the ultmiobranchial 

 body from the fourth pouch. 



Rabl ('07) was the first to demonstrate the existence of two 

 distinct diverticula in connection with the posterior wall of the 

 fourth pouch, one of which represents the true fifth pouch and 

 the other the anlage of the ultimobranchial body. His observa- 

 tions were made on the duck. The ultimobranchial diverticu- 



