Plate XXIV. 



Fig. 10. Sec. No. 278. G. IX. A high power drawing of the most anterior 

 section of Gang. IX in which there is contact with the ectoderm. The placodal 

 thickening is quite marked and there is some evidence of active proliferation in 

 the placodal area. The cells of the placodal component are smaller than those of 

 the general visceral portion. There are a few cells near the ectoderm which have 

 evidently been recently contributed from the placode and have not yet undergone 

 metamorphosis. 



Fig. 11. Sec. No. 280. G. IX. In this section, the smaller size of the nuclei of 

 placodal cells is quite marked. The outline of the general visceral component is 

 easily distinguishable throughout part of the extent of the contact with the pla- 

 codal portion. Here again, may be seen a small mass of undifferentiated placodal 

 cells lying near the ectoderm. 



Fig. 12. Sec. No. 281. G. IX. In this section, the metamorphosing cells are 

 completely surrounded by undifferentiated cells. The presence of mitotic figures 

 indicates active proliferation. 



Fig. 13. Sec. No. 282. G. IX. The extent of the contact with the ectoderm is 

 greater than in the previous section. Proliferation must be going on more rapidly 

 than metamorphosis, since the mass of undifferentiated cells near the ectoderm 

 is larger and shows the cells massed more closely and tending to form lamellae. 



Fig. 14. Sec. No. 284. G. IX. In this section, proliferation is very rapid as 

 evidenced by the large mass of imdifferentiated cells and the comparatively 

 narrow field of placodal cells which have undergone metamorphosis. The marginal 

 extent of contact is shorter than in the more anterior sections. 



Fig. 15. Sec. No. 286. G. IX. The contributed portion of the ganglion is very 

 large in proportion to the size of the general visceral ganglion. Several mitotic 

 figures may be seen and there is a well marked margin of undifferentiated cells. 

 The placodal thickening is dorso-lateral to the contact area which is still shorter 

 in extent than in Fig. 14. 



Fig. 16. Sec. No. 289. G. IX. The extensive placodal thickening still persists 

 and active proliferation is still going on. 



Fig. 17. Sec. No. 275. G. IX. This section .shows the relation of the lateralis 

 and visceral components anterior to the point of contact. It is, here, impossible 

 to distinguish the placodal thickening from that accompanying the gill cleft 

 opening, which lies ventral to it. 



Fig. 18. Sec. No. 278. G. IX. An outline drawing of the same section as Fig. 



10. The lateral line placode is very distinct from the epibranchial placode. The 

 epibranchial placode, since the gill cleft is open, is easily distinguishable from the 

 gill cleft thickenings of the ectoderm. 



Fig. 19. Sec. No. 280. G. IX. An outline drawing of the same section as Fig. 



11, showing the relation of the contributed mass to other structures. 



Fig. 20. Sec. No. 287. G. IX. An outline drawing one section posterior to Fig. 

 15, showing the dorso-lateral point of contact. 



Fig. 21. Sec. No. 296. G. IX. Showing the appearance of the lateralis com- 

 ponent of Gang. X, the great thickness of the lateral line placode, and the relative 

 size of the placodal and general visceral portions of Gang. IX. 



