CRANIAL GANGLIA OF AMBLYSTOMA 471 



sufficiently to say definitely how much is really lacking. The 

 gasserian ganglion is much smaller in this individual. The cera- 

 tohyoid procartilage is normal on the operated side. In all cases 

 where such an area as just described was removed there always 

 appeared the same results, viz., a very small ganglion whose 

 slender fibers supplied sense organs on the side of the head and 

 lower jaw was the only representative of the VII ganglion. 



6. Removal of epibranchial placodes of IX and X and postaudi- 

 tory lateral-line primordia. The operations were done around 

 stages 21 and 26 and involved the removal of varying amounts of 

 ectoderm posterior to, and often including, the auditory placode. 

 The most satisfactory results were obtained in removing ectoderm 

 outlined in the manner shown in figure 58. 



Whenever the upper posterior border of the gill swelling was not 

 removed (fig. 59) there appeared a small ventral body line of 

 sense organs (fig. 60), although the dorsal and midbody lines 

 were entirely absent. This occurred in many specimens and 

 indicates, as shown in the descriptions of the normal material, 

 that there is a separate placode for the ventral body line. 



In a number of cases the occipital group of sense organs occum 

 (fig. 61), although the auditory vesicle was removed. The 

 anterodorsal portion of the gill swelling was not well covered 

 according to an observation of the blue ectoderm two days after 

 the operation. The occipital or ventral body lines may persist 

 after the operation, but only after operations done around 

 stage 21. It appears that the area capable of regenerating these 

 primordia is diffuse at this early stage. 



Fig. 61 Camera drawing, showing only a few sense organs of occipital group 

 when not all ectoderm is removed over anterodorsal portion of gill swelling. No 

 dorsal nor midbody line of sense organs is present. X 10. 



Fig. 62 Camera drawing, showing in dotted line twelve hours after operation 

 at stage 26 the area of ectoderm removed, including all postauditory lateral- 

 line primordia and epibranchial placodes. X 10. 



Fig. 63 Camera drawing of embryo figured in 71, showing thirteen days after 

 operation the extent of blue ectoderm and absence of postauditory lateral-line 

 sense organs. X 10. 



Fig. 64 Frontal" section of the embryo shown in figure 63, showing normal 

 branchial arches. X 37. 



Fig. 65 Frontal section through similar level on either side, showing the 

 small visceral ganglion of X on the operated side. X 37. 



