40() F. L. LAND ACRE 



EXPLANATION OF FIGURES 



09 (A. melas, 93 hours) is taken through the detached portion of epibranchial 

 ganglion IV, also shows the root of epibranchial ganglion III. 



70 (A. melas, 93 hours) is taken through the fourth epibranchial ganglion just 

 before it comes into contact with the lateral mass ganglion of the X (general com- 

 munis X). In fig. 70 the root of the third epibranchial ganglion has become so 

 attenuated that it cannot be recognized with certainty, alhough the two cells 

 marked Ep. gl. Ill appear to be the posterior extension of this ganglion. 



71 (A. melas, 93 hours) shows the point of union of the fourth epibranchial gan- 

 glion with the lateral mass of the X (Gen. vis. X). 



7(i. 72, 73 and 74 illustrate the conditions under which the fifth and sixth epi- 

 branchial placodes arise. In fig. 70 (A. melas, 93 hours) the fifth epibranchial 

 placode appears before the lateral mass ganglion of the X comes into contact with 

 the epidermis. In fig. 72 (A. melas, 99 hours) the attachment is quite like that in 

 fig. 73 (A. melas 105 hours). In both these cases the attachment of a lateral 

 mass (neural crest) ganglion to the epidermis is quite evident and corresponds 

 to the oft repeated descriptions in the literature of the contact formed between 

 neural crest ganglia and the epidermis. Nothing resembling this occurs in 

 Ameiurus except in the fifth and sixth epibranchial placodes. 



74 (A. melas, 113 hours) is taken through the attachment of the general com- 

 munis X to the sixth epibranchial placode. 



75 to 78 illustrate the formation of the jugular ganglion of the Xth. Fig. 75 

 (A. melas, 69 hours) shows the slight condensation of cells in the future position 

 of the jugular ganglion before the appearance of the root of the X. 



76 (A. melas, 81 hours). The cells which later form the jugular ganglion inclose 

 the fibrous root of the X. 



77 (A. melas, 113 hours) shows the first decided increase in size of the jugular 

 ganglion when it begins to mass itself into definite areas of cells such as appear in 

 fig. 78 (138 hours) where the ganglion is broken into small masses by the fibrillated 

 root of the X. 



