KvS IVAN E. WALLIN 



('Ilium coiiiuM'ts tlu^ thyreoid witli the fifth pouch. In the 

 seventh ])ou('li the cihated groove ends. It is (Hrc^ctly continued 

 by non-cihatetl epithehuni which, in a few sections caudad, 

 becomes a ridge. The cihated groove is a continuous groove 

 from the fourth to the seventh pouches. The ridge which be- 

 gins in the seventh pouch gradually becomes high and stalked 

 in the eighth pouch. The median columnar epithelium becomes 

 invaginated and is directly continuous into the floor of the oesoph- 

 agus. Surrounding the junction it seems to me there is evi- 

 dence of a vestigial eighth gill arch in w-hich an aortic arch is not 

 present. The respiratory part of the branchial cavity extends 

 a short distance caudad of the point of junction betw^een the 

 pharynx and oesophagus. 



The dorsal ciliated grooves arising in the diverticula follow 

 the course of the first aortic arch to the median dorsal line of the 

 pharynx. They fuse at this point to form a single ciliated band 

 which extends caudally the whole length of the branchial cavity 

 and w^hich is directly continuous into the roof of the oesophagus. 

 A short distance caudad of the point of origin, this band forms a 

 rounded ridge which extends to the seventh sac w^here it is 

 converted into a groove. The aorta is lodged in the concavity 

 of the rounded ridge. At the point where the tw^o dorsal grooves 

 of the first pouch fuse a tongue-like piece of non-ciliated epithe- 

 lium is pinched off (text fig. 2). Schaffer apparently mistook 

 this for ciliated epithelium and considered it the end of the fused 

 ciliated bands. 



The first pair of gill arches come together dorsally in the 

 median line. Their ventral extremities, however, are far apart 

 and end in the ventro-lateral part of the respiratory pharynx. 

 Gill lamellae are present only on the caudal surface of the first 

 gill septum. The second pair of arches are farther apart and 

 thus they differ from the remaining caudal arches. Their dorsal 

 attachments are in the angle between the epipharyngeal ridge 

 and the dorso-medial part of the respiratory pharynx. \'en- 

 trally, the second gill arches are attached about midway between 

 the mid-ventral line and the ventro-lateral angle of the respira- 

 tory pharynx. The dorsal attachments of the third and remain- 



