8 F. L. LANDACRE 
Dohrn (’02) gives a full description with numerous figures of 
the migration of the neural crest ventrally into the branchial 
region and its metamorphosis into mesenchyme and cartilage of 
the branchial bars in Torpedo ocillata. He agrees fully with 
Miss Platt’s interpretation of the origin of branchial cartilages 
from ectoderm, although he derives them from the neural crest 
rather than from the lateral ectoderm. He does not exclude the 
contribution of the cells from the lateral ectoderm in later stages, 
although neither his figures nor text include such a contribution. 
He adopts Miss Platt’s term mesectoderm and criticises the 
effort of Corning to maintain the integrity of the germ layers in 
the formation particularly of structures derived from the meso- 
derm. Dohrn’s evidence for the derivation of connective tissues 
and cartilage from ectoderm is more convincing, if possible, than 
that of Brauer in the Gymnophiona and of Kupffer in Petromyzon, 
both of whom give detailed descriptions. Dohrn’s figures taken 
with Neal’s (’98) reconstructions of Squalus (figs. 7 to 21, pls. 
3 and 4) furnish convincing evidence for the continuous migra- 
tion ventrally (Neal) of the neural crest and its ultimate trans- 
formation into permanent mesenchyme and cartilage of the 
branchial bars (Dohrn). 
Brauer (’04), working on the Gymnophiona, derives mesen- 
chyme of the anterior region of the head from neural-crest cells 
which later mingle with cells derived from endoderm to form 
mesenchyme in which the two derivatives cannot be recognized 
after this fusion. He can find no evidence for the disappearance 
of these neural-crest cells, however, before their fusion with 
cells derived from the endoderm. In the posterior head region 
neural-crest cells, when not involved in the formation of ganglia, 
grow ventrally into the branchial bars and surround the meso- 
derm of the bar at first lying on its lateral surface, but finally 
entirely surrounding it. He can find no evidence for the deriva- 
tion of mesenchyme in the gill bar from the adjacent lateral 
ectoderm, as Miss Platt had done, but derives it entirely from 
the neural crest. He does not deny the possible later mingling 
of cells derived from mesoderm with those derived from the 
neural crest, but insists that the chief part in the formation of 
