pericardial rudiiBent . P. 2. 



Pig. 10. Transverse section through posterior end of bud, 



showing an early stage in the displacernent or shift- 

 ing of the inner vesicle. The wall of the latter 

 is being bent in at the point indicated by tne line 

 a. D. 2. 



Pig. 11. Transverse section through posterior end of bud 



slightly older than last, showing further progress 

 of the displacement of the vesicle. The peribran- 

 chial rudiment is at a much lower level than in the 

 last figure, and the wall of inner vesicle is being 

 bent in further at a_. D. 2. 



Pig. 12. Transverse section through the middle region of 



same bud as the one shov/n in Pig. 11. The section 

 lies in front of the connection with the stolonic 

 partition, and shov/s the beginning of the fold 

 which will form the right peribranchial cavity. 

 D. 2. 



Pigs. 13-18. Series of transverse sections of a bud at 



about the same stage as that shown in Pig. 4. "^he 

 sections are taken respectively at the levels in- 

 dicated by the lines, a, _b, £, d, _e and f, in Pig. 

 4. Pig. 1-', line a, the most anterior secticn, 

 shows undivided portion of branchial sac, and dor- 

 sal tube. "Pig. 14, line b, is a little furtner 

 back and shov/s anterior extension of right peri- 

 branchial cavity. Pig. 15, line _c, is taken imme- 



•74- 



