624 



To recur to the question of the interpretation of this structure 

 as a vestigial organ. The method of its development, I believe, throws 



3 mrr\ 



5 mi 



S.4 



10 tnm 



11(13) mm (l) 



mm 



IG-nmrn 



21 mm 



Fig. 9. A series of diagrams illustrating the changes in form undergone by 

 the caudal pharyngeal complex. The connection with the ectoderm,— where it 

 exists,— is shown by oblique lining, the parathyroid area by stippling, x indicates 

 the recently broken connection of the complex with the cervical vesicle; the con- 

 dition upon the other side being shown in the proceeding figure. iF fourth pouch; 

 it ultimobranchial. 



