Plate XXV. 



Fig. 22. Sec. No. 320. G. Xi. Showing the contact point just mesial to the 

 •external opening of the gill cleft. There are no mitotic figures in the contributing 

 area, but there may be seen a very definite zone of metamorphosing cells along 

 the lateral border of the ganglion. 



Fig. 23. Sec. No. 324. G. Xi. Two points of contact are seen and proliferation 

 is going on quite rapidly, from the fact that there is a large mass of larger and 

 more clearly stained cells between the two points of contact and external to the 

 metamorphosing zone. The outline of the visceral portion of the ganglion is only 

 fairly distinct. 



Fig. 24. Sec. No. 326. G. Xi. The mass of metamorphosing cells is almost 

 surrounded by undifferentiated cells. This, together with the presence of mitotic 

 figures, indicates active proliferation froin the placodal area. 



Fig. 25. Sec. No. 323. G. Xi. An outline drawing of the section anterior to 

 Fig. 23, showing the general topography and the relation of the ganglion to the gill 

 cleft and the placode, the latter being indistinguishable from the ectodermal 

 thickening accompanying the opening of the gill cleft. 



Fig. 26. Sec. No. 345. G. X. This section shows the relation of the main 

 ganglion to the ectoderm and the gill groove. The second epibranchial ganglion 

 of X, G, V, X2, is seen partly constricted off from the main ganglionic mass. A 

 lateral line nerve is seen leading to the easily distinguished lateral line organ. 



Fig. 27. Sec. No. 350. In this figure, the epibranchial ganglion is seen lying 

 close to a thickening in the epithelial lining of the pharyngeal gill pouch. This 

 thickening is continuous, in later sections, with the placodal thickening of the 

 ectoderm, posterior to the point at which the gill cleft is entirely open. 



Fig. 28. Sec. No. 351. The endothelial thickening persists and is nearer the 

 external aperture of the gill cleft. 



Fig. 29. Sec. No. 352. The endothelial thickening is more clearly defined 

 than in the previous section. 



Fig. 30. Sec. No. 352. G. X2. A high power drawing of the same section as in 

 the preceding figure, showing proliferation and a mass of cells with darkly stained 

 nuclei which are not appreciably smaller than those of the cells of the general 

 visceral ganglion. The oval outline of the general visceral portion and the 

 boundary between this and the placodal portion are clearly seen. 



Fig. 31. Sec. No. 353. G. X2. Here the placodal thickening is clearly seen 

 and there is much evidence of active proliferation. 



Fig. 32. Sec. No. 357. G. X.. The placodal thickening is still seen but the 

 extent of contact with the ganglion is slight. The placodal cells constitute a much 

 larger mass than the general visceral cells. 



Fig. 33. Sec. No. 357. G. X2. An outline drawing of the same section as shown 

 in Fig. 32. 



Fig. 34. Sec. No. 375. G. X3. An outline drawing of a section anterior to the 

 point of separation of the epibranchial ganglion from the main ganglionic mass of 

 X; also anterior to the anterior extremity of the gill cleft, showing the lateralis 

 component and a branch to the lateral line placode. 



Fig. 35. Sec. No. 378. G. X3. The outline of the general visceral component is 

 fairly distinct and the mass of placodal cells relatively large; there is no contact 

 withjthe ectoderm and it is impossible to distinguish the placode from the gill 

 cleftithickenings. 



Fig. 36. Sec. No. 380. G. X3. The mass of contributed cells is very large but 

 the placode is still indistinguishable from the gill cleft thickenings. 



Fig. 37. Sec. No. 381. G. X3. The general visceral portion of the ganglion is 

 relatively small; there is evidence of active proliferation and a small area of 

 contact but the extent of the placodal thickening is small. 



Fig. 38. Sec. No. 383. G. X3. The placodal thickening is ciuite marked and 

 there is much evidence of active proliferation. The outline of the general visceral 

 portion of the ganglion is quite distinct. 



