DEVELOPMENT OF SUPRAPERICARDIAL BODY 381 



tached to the caudal and lateral portion of the ventral mass 

 giving the gland a direction of growth which is distinctly medial 

 and forward. The lumen of the stalk communicates with that 

 of the vesicle and with the pharynx. The attachment of the 

 stalk to the pharyngeal epithelium is very much constricted and 

 is indicated by a small depression in the ventral pharyngeal wall. 



From the 33 to the 37 mm. stage the suprapericardial body 

 shows great advance in development. In the series of five 

 embryos studied of this stage (S. C. 25; S. C. 10; S. C. 9; H. E. 

 C. 186 and H. E. C. 363) the bodies were found only on the 

 left side. They have about the same position as in the preced- 

 ing embryo. The form of the gland is shown in figure 22 from 

 a wax reconstruction ol the left gland of a 37 mm. embryo (H. 

 E. C. 363). The ventral portion consists of an elongated thin- 

 walled vesicle running parallel to the long axis of the pharynx. 

 It is constricted at its middle and terminates posteriorly in two 

 rounded knobs. A small bud is arising on its medial surface. 

 The connecting-stalk is long and angular and is attached to the 

 dorsal, caudal portion of the vesicle. A small bud which arises 

 from the stalk is directed cranialward. The lumen of the con- 

 necting-stalk is small and irregular and does not communicate 

 with the pharyngeal cavity nor with the cavity of the vesicle. 

 As is shown in the above description, two important features 

 appear in the gland at this stage (36-37 mm.). They are the 

 beginning formation of new tubules by budding and a disap- 

 pearance of the earlier communication found between the ven- 

 tral portion of the gland and the pharynx. 



At 47.3 mm. (S. C. 11 and others) the suprapericardial body is 

 again found on both sides. The right gland is very small and 

 is situated at about the level of the cranial extremity of the left 

 gland (fig. 4). The caudal portion of the pharynx at this stage 

 has become arched from side to side because of the dorsal bulg- 

 ing of the heart. This change in the contour of the pharyngeal 

 wall has caused the suprapericardial body to assume an oblique 

 position, being directed medially and ventrally from its attach- 

 ment to the pharynx. Immediately below the sixth pouches 

 the pharynx becomes abruptly constricted transversely to form 

 the oesophagus. 



