404 F. L. LANDACRE 



EXPLANATION OF FIGURES 



57 is taken one section posterior to fig. 56 at the point where the ganglionic mass 

 is free from the epidermis. 



58 and 59 are taken through the root of the epibranchial ganglion of the IXth 

 just before it comes into contact with the lateralis and motor portions of the IX, 

 as shown in fig. 59. 



60 (A. melas, 93 hours) is taken through the epibranchial ganglion at the nearest 

 point of approach to the epidermis. This is the first stage in which the ganglion 

 is completely detached from the epidermis. Its clean cut boundaries during all of 

 its development indicate that no other cells than those derived from the placode 

 are incorporated in the ganglion. 



61, 62 and 63 (A. neb.) illustrate three stages in the formation of the lateralis 

 IX ganglion of which fig. 63 (A. neb., Stage V) is the earliest. The ganglion varies 

 a great deal in appearance and somewhat in position. Fig. 62 (A. neb., Stage IX) 

 is older than fig. 61 (A. neb., Stage VIII). Fig. 63, while taken from the posterior 

 end of the vesicle, differs totally from the appearance of this region before and after 

 the formation of the ganglion. 



64 to 71 show the formation of the first two epibranchial ganglia of the X. 



6-4 (A. melas) 69 hours shows the earliest recognizable trace of the third epi- 

 branchial placode. Figs. 65 to 71 are from the same embryo (A. melas, 93 hours). 



65 is through the anterior portion of the placode. 



66 is through the middle region just before the detached portion is reached. 



67 is just backof the point of detachment. 



68 is through the root of the third epibranchial ganglion and the fourth epi- 

 branchial placode. This probably is not the earliest trace of the fourth epibran- 

 chial placode, however. The preceding series is defective at this point. 



