connection v/ith the stolcnic partition. D. 2. 



Pigs. 22, a and b. These sections illustrate the develop- 

 ment of the .^ill-slits . Tn a, tiie thickened bran- 

 chial wall is slightly cvaginated and is in contact 

 with the thickened patch of cells in the visceral 

 wall of the peribranchial cavity. The lov/er por- 

 tion of h^ shov/s the fusion between the two walls, 

 and the upper portion, a stage after the formation 

 of the opening. P, 2. 



Pigs. 23, a and b^. Stages in the formation of the branchial 

 orifice. In a, the much-thickened invaginated ec- 

 toderm is seen nearly touching the branchial v/all. 

 The fusion of the two walls is shov/n in _b. P. 2. 



Pig. 24. Transverse section through the extreme posterior 

 end of a bud, showing the origin of the gut, as a 

 diverticulum on the left side of the branchial sac. 

 D. 2. 



Pig. 25. Section through the wall of the stomach and a por- 

 tion of the duct of the "organe refringent", snov/- 

 ing clearly the connection of the latter with the 

 digestive tract. ?. 2. 



Pig. 26. Transverse section of the terminal portion of the 



. intestine, soov/ing the surrounding ducts and ampul- 

 lae of the "organe refringent" with tneir deeply 

 stained nuclei. 7. 2. 



Pig. 27, a, b, c^, d, and e_^ Sections illustrating the devel- 

 opment of the pericardium. i is from a frontal 



