PLATE 7 
Fig. 34 from an 82 hr. embryo is taken through the posterior portion of the thick- 
ening of the ectoderm at the point where the endoderm of the pharyngeal gil | 
pocket joins it. The ectoderm is easily distinguished by its color. 
Fig. 35 from an 82 hr. embryo is taken through the thickening in the epidermis 
just posterior to the hyoid gill pocket and is presumably the anterior extension of 
the preauditory placode and, although it is not detached from the auditory ves- 
icle, it shows none of the histological characters of the preauditory placode. Fig. 
35 les three sections posterior to fig. 34. 
Fig. 36 from a 94 hr. embryo, is taken at the extreme posterior limit of the con- 
tact of the pharyngeal gill pocket with the ectoderm. The nuclei of the ectoderm 
are closely packed and the cell walls are indefinite or absent, showing distinctly 
that it is related to the epibranchial placode rather than to the preauditory pla- 
code. ; 
Fig. 37 from a 94 hr. embryo is taken just posterior to the contact of the hyoid 
gill pocket with the ectoderm and shows the proliferation of cells to form the epi- 
branchial placode. Fig. 37 is the next section posterior to 36. - 
Figs. 36 and 37 show the absence of any primordium of the lateral lines in the 
region of the placode up to this age. 
Fig. 38 from a 7.3 mm. embryo is taken at the posterior limit of the contact 
of the hyoid gill pocket with the endoderm. In addition to the ectodermice gill 
thickening there is a dorsal thickening (primordium of lateral line). 
Fig. 39 from a 7.3 mm. embryo is taken just posterior (two sections back of fig. 
38) to the contact of the hyoid gill pocket with the ectoderm. It shows three 
thickenings; most dorsal, the primordium of the lateral line; most ventral the prob- 
able remnant of the preauditory placode. The middle thickening is the epi- 
branchial. 
62 
