CEAXIAL GANGLIA OF AMBLYSTOMA 465 



Due to the inability to locate exactly the position of the audi- 

 tory placode, especially in stage 21, it was often included wholly 

 or in part in the excised ectoderm. Among such cases where the 

 auditory vesicle was not entirely absent, it appeared as a small 

 rudimentary vesicle near the skin. 



An examination of specimens which were treated in the manner 

 just described shows in eight cases no supra-orbital group of 

 lateral-hne sense organs (fig. 47), and consequently no ophthal- 

 micus superficialis VII nerve. The operations in seven of these 

 cases were performed at stage 23 and in one case about stage 21. 

 The auditory vesicle appears as a rudiment in six cases, while in 

 the other cases it is entirely absent. The larger portion of the 

 lateral-line ganglion of VII which supplies nerve fibers to the 

 supra- and infra-orbital groups of sense organs is represented in 

 these cases by a very small ganglion. The infra-orbital line of 

 sense organs with its corresponding nerve was never absent in 

 this type of operation and it received its fibers from the small 

 remaining portion of the above-mentioned lateral-hne ganglion. 



In a few cases where a small portion of the placode was, pre- 

 sumably, not entirely extirpated, the VII lateral-hne ganglion is 

 smaller than on the normal side and a small hne of sense organs 

 is the only representative of the supra-orbital line (fig. 48). In 

 some cases a sensory line was represented by small, poorly de- 

 veloped organs and the ophthalmicus superficialis VII is so slender 

 that it can be followed with great difficulty and then only when 

 most favorably stained. Such cases show diminution in the size 

 of the VII lateral-line component which supplies the supra-orbital 

 and infra-orbital sensory lines. Throughout all these cases in 

 which the supra-orbital sensory line is represented in part or in 

 its entirety the ear is present and apparently normal in size. 



The hyomandibular, ventral, and mandibular groups of lateral- 

 hne sense organs were never disturbed when such an area of 

 ectoderm was removed. The VII lateral-line component of the 

 ganglion supplying nerves to these groups was always normal. 

 It is quite apparent that no other portions of the VII ganglion 

 are lacking. 



