584 F. L. LANDACRE AND A. C. CONGER 



of the line show the characteristic radial arrangement of the sen- 

 sory lines much more plainly at some points than at others. 

 These points mark the positions of future lateral line organs. 

 The infra-orbital line begins behind and ventral to the posterior 

 end of the supra-orbital line, and runs cephalad and ventrad in a 

 curve which follows, in general, the outline of the optic vesicle. 

 The infra-orbital line ends anteriorly at a point ventral to the 

 anterior end of the oj^tic vesicle and at the level of the ventral 

 border of the olfactory capsule. 



Owing to the angle of sectioning, the cells of the mandibular 

 line do not exhibit the characteristic radial arrangement in so 

 marked a degree as the cells of the supra-orbital and infra-or- 

 bital lines. The mandibular line begins in the region of the hyoid 

 gill and may be traced cephalad and sharply ventrad until it is 

 lost in the thickened epithelium where the embryo joins the yolk 

 sac. 



No trace of an anastomosis could be noted at this stage, either 

 between the supra-orbital or sub-orbital Unes, or between these 

 and the mandibular line. 



In the postauditory region of the 8.5 mm. embryo there are 

 three lateral line primordia. The first and most anterior is not 

 strictly postauditory in position but lies in the region of the pos- 

 terior third of the auditory vesicle and its organs are inner \ated 

 by the ramus supratemporalis X. The second extends forward 

 from the anterior end of the lateralis X ganglion and in a vertical 

 axis lies over the second gill and its organs are innervated by the 

 ramus supratemporalis X. The third extends from the posterior 

 end of the lateralis X ganglion toward the posterior end of the 

 body. Its organs are innervated by the main lateral line ramus 

 of the X ganglion. 



EARLY STAGES 



No attempt has been made to trace carefully the very early 

 stages in the development preceding the appearance of the pri- 

 mordium of the auditory vesicle and the preauditory placode, 

 since that problem is not within the scope of this paper as it in- 

 volves the origin of cranial ganglia not related to the sensory 



