PLATE 8 



EXPLANATION OF FIGURES 



29 Stage XVI, age 88 hours. A camera outline taken through the contact of 

 the second true gill with the ectoderm. The posterior extension of the first true 

 gill thickening, Ec.Th. 1, is pronounced in this series. The second endodermic gill 

 pocket touches the more ventral thickening which in figure 28 is labelled A /ij/.T/i. 

 This section lies, in the longitudinal axis, near the middle of the two thickenings 

 of figure 1, at which point they overlap. 



30 Stage XVII, age 94 hours. A camera outline taken through the area of 

 contact of the second true gill pocket, and the anterior end of the angular thick- 

 ening. The section is taken through the anterior end of the second postauditory 

 ectoderm thickening of figure 2. The region marked Ang.Th. in figure 30 is actually 

 no thicker than the intermediate region lying between it and the area of contact, 

 Ec.Th. 2, but it is in the exact position of the angular thickening (Ang.Th.) of fig- 

 ure 31. X 75. 



31 Stage XVIII, age 94 hours. A camera outline just behind the area of con- 

 tact of the second true gill pocket. The third gill pocket is not yet in contact 

 with the ectoderm and the more ventral thickening is consequently labelled an- 

 gular thickening (Aiig. Th.), but it represents the area of contact of the third true 

 gill pocket. X 75. 



32 Stage XXI, age 120^ hours. A camera outline taken near the posterior 

 end of the auditory vesicle, and behind the first gill slit in the posterior extension 

 of the thickening of this slit, Ec.Th. 1. The primordium of the lateral line, Po.L.L. 

 is close to the lateralis IX ganglion, but not so close as at the posterior end of 

 the primordium. For note on figures 32 and 5, see next paragraph. X 75. 



33 Stage XXI, age 120^ hours. A camera outline taken through the extreme 

 anterior end of the lateralis X ganglion and the extreme posterior end of the thick- 

 ening extending behind the second gill. There seems to be discrepancy between 

 figures 32 and 33 and figure 5, in that figures 32 and 33 show a gill contact overlap- 

 ping the preceding lateral line primordium, while in figure 5, for instance, the 

 first lateral line primordium does not overlap the second gill contact. This ap- 

 parent discrepancy is due to the fact that in figure 5, as in all reconstructions 

 (figs. 1-6) gill contacts are not shown on the plot unless there is a noticeable thick- 

 ening of the ectoderm in the region of contact. The contacts {con.2 and con.S) 

 on figures 32 and 33 are contacts simply with no thickening of the ectoderm. X 75. 



34 Stage XXI, age 120^ hours. Camera outline taken at posterior end of 

 lateralis X ganglion and behind the fourth gill contact of figure 5. This section 

 lies near the posterior end of the thickening extending back from the fourth gill 

 contact and, since the fifth gill contact is not yet found, is labelled angular thick- 

 ening. X 75. 



632 



