24 F, L. LANDACRE 
d. The lateral ectoderm also gives rise to the lateral-line 
primordia (placodes) which are distinct structures, although in 
some types closely related in time of appearance and sometimes 
even in position with other structures derived from the lateral 
ectoderm. If followed carefully, however, their identity can be 
established with certainty. Their thickenings or placodes are 
usually accompanied by detached cells and should not lead to 
confusion as to their fate. 
e. Next the lateral ectoderm gives rise to the epibranchial 
placodes which furnish the special visceral or gustatory portions 
of the VII, IX, and X ganglia. Since these placodes become 
completely detached from the lateral ectoderm and added to 
the neural-crest portions of the VII, IX, and X ganglia and do 
not always have definite boundaries, they might be misinterpreted 
as contributions of the lateral ectoderm to mesenchyme in the 
branchial region. If these placodes are followed carefully they 
are found to have nothing to do with mesenchyme, but are 
ganglion-forming structures. 
Aside from the oral region, which must be taken up more in 
detail, these five structures are all that might be mistaken for 
contributions to the mesenchyme. ‘The point to be emphasized, 
aside from our own observation, is this: any claim that the lateral 
ectoderm contributes to the formation of mesenchyme that does 
not take into consideration and account for the structures 
mentioned above is open to serious criticism. We believe that. 
the disagreement among authors as to the exact condition in the 
lateral ectoderm is due to failure to account for the structures 
enumerated above before assuming that cells delaminated from 
the lateral ectoderm went into the formation of mesenchyme. 
With the facts mentioned above in mind, we have examined 
carefully our series and, aside from the oral region yet to be 
described, we can find no evidence for the contribution of lateral 
ectoderm cells to mesenchyme. In fact, the ectoderm at all 
points except those mentioned is intact and shows no indication 
of liberating cells, and we find ourselves in the closest accord 
with the statements of Dohrn (’02) and Brauer (’04), who can 
find no such contribution. 
