CHRONOLOGICAL SUMMARY OF ORGAN ANLAGEN 



253 



Stage 22: 8 mm. total body length. 



Heart partitions completed and heart differentiated, circulation 

 reaches tail fin, lung buds develop, sub-notochordal rod disappears 

 and mesonephros begins to form. 



< ■■ ■ .■■■■■iC^- - - --^ 





Olfactory organs of Rana pipiens tadpoles at 20 mm. total body length. 



(af) Anterior choanal fold, 



(cc) Choanal canal, 



(ct) Cornu trabeculae. 



(cv) Christa ventralis. 



(ec) Entrance canal, 



(ig) Inferior canal. 



(ir) Inferior recess. 



(b) Lateral appendix. 



(Ig) Lateral groove. 



(pf) Posterior pharyngeal fold. 



(pr) Posterior recess. 



(sc) Superior cavity. 



(Courtesy, Ruth Cooper, /. Exper. ZooL, 93:415.) 



