396 F. L. LAX I) ACRE 



EXPLANATION OF FIGURES 



10 and 11 (A. neb. . Stage V) are from the same embryo. Fig. 10 is taken through 

 the posterior end of the Gasserian ganglion at one of the earliest stages at which 

 it can be definitely located. This section passes through the hyoid gill pocket 

 (En.). 



11 is taken through the posterior end of the lateralis VII ganglion and lies four 

 sections anterior to the auditory vesicle. 



12 (A. neb., Stage VII) is from an older embryo than that from which fig. 6 

 was taken. It lies in the mid-region of the vesicle and shows the absence of a lat- 

 eral mass after the vesicle is formed. 



13 is taken from the same embryo as that from which figs. 10 and 11 were taken 

 (A. neb., Stage V). It lies four sections back of the anterior end of the auditory 

 vesicle. The proliferation of the capsule cells to form the auditory ganglion 

 is taking place here. 



14 and 15 (A. neb., Stage IV) are from embryos of the same age. Fig. 14 lies 

 two sections anterior to the anterior end of the auditory vesicle. The preaudi- 

 tory placode is here continuous with the vesicle; on the opposite side of the same 

 embryo there is one section, fig. 15, intervening between the preauditory placode 

 and the vesicle. 



16 (A. neb., Stage IV) is from a slightly more developed embryo of the same age 

 as figs. 14 and 15 and is taken through the middle of the preauditory placode. There 

 are six sections in which the placode is absent between the posterior end of the 

 placode and the anterior end of the vesicle. 



17 (A. neb., Stage V) is taken from an older embryo than the one from which 

 fig. 16 Is taken and lies nineteen sections anterior to the vesicle. The placode is 

 here disintegrating and is entirely absent in the remaining eighteen sections. It 

 is intact anterior to this point. 



18 from the same embryo as fig. 17 shows the appearance of the preauditory 

 placode at the posterior third of its contact with the hyoid gill pocket which ex- 

 tends over eleven sections. This is the last recognizable stage of the placode. 

 It still retains a slight resemblance to the earlier stages. 



19 to 24 (A. neb., Stage VI) are all from the same embryo. Fig. 19 is taken 

 through the mid region of the hyoid gill pocket and shows the complete disappear- 

 ance of the preauditory placode. 



20, 21, 22 and 23 are consecutive sections, fig. 20 lying at the extreme posterior 

 end of the point of contact of the hyoid pocket whth the epidermis. The small 

 mass of cells (X) lies anterior to the position of the future epibranchial ganglion 

 and does not seem to enter into its composition. These sections show the gradual 

 thickening and irregular arrangement of the cells in the epidermis (epibranchial 

 placode) which precedes the proliferation of cells mesially. 



