DEVELOPMENT OF SUPRAPERICARDIAL BODY 383 



formed of a large tubule (C) and a broad flattened vesicle (D). 

 These two masses are united at their caudal extremities and 

 have a common cavity. Both C and D give rise to small tubules 

 and epithelial buds. A comparison of figures 22 and 24, shows 

 that in older embryos the connecting-stalk has become broken 

 into segments which correspond to A, B and C. The ventral 

 vesicle has steadily increased in size and now gives rise to a few 

 small tubules. It still retains its connection with the stalk- 

 element (C). In a slightly older embryo, 50 mm. long, (H. E. 

 C. 444) these changes have become somewhat more marked. 

 The growth of the gland has been chiefly in its cranio-caudal 

 axis. The ventral A^esicle has become very much elongated. 

 The stalk-element is represented by many small tubules and 

 buds, one of the most dorsal of which unites with the pharyngeal 

 epithelium . 



The position of the gland at 60 mm. (H. E. C. 427) is shown 

 in figure 5. It is attached to the wall of the pharynx by a rather 

 long tubule and also by a small cord of epithelial cells situated 

 just caudal to the tubule. It has the same general form as in 

 the 50 mm. embryo but has many more newly-formed tubules, 

 some of which are completely isolated and lie in the mesen- 

 chyma of the pharyngo-pericardial wall. 



The oblique position of the gland and its shift to a more 

 medial position, which were first noticed in the 33.1-47.3 mm. 

 embryos, have become more pronounced at 95 mm. (H. E. C. 

 1882). These features are shown in figure 6, from a wax model 

 of the caudal portion of the pharynx at this stage. There is a 

 rather sharp ventral outpouching of the wall of the pharynx 

 just lateral to the suprapericardial body on either side. It begins 

 just above the attachment of the gland and runs obliquely out- 

 ward and backward parallel to the ventral diverticulum of the 

 sixth pouch. On the dorsal wall of the pharynx, and forming 

 its caudal extremity on either side, are two outpouching^ very 

 similar to those described above. These outgrowths, both dorsal 

 and ventral, were first found in an embryo 80 mm. in length (S. C. 

 60). They are parallel to the corresponding extremities of the 



