OEIGIN OF THE LATERAL LINE PRIMORDIA 577 



Lepidosteus osseus was chosen for this study on account of its 

 systematic position, and particularly on account of the fact that 

 it has well defined sensory lines preceding the appearance of 

 lateral line organs. 



HISTORICAL REVIEW 



The papers of Froriep ('85) and of Beard ('85 '88) while they 

 do not bear directly on the relation of the sensory lines to the 

 auditory vesicle, are still of interest in view of the variety of 

 structures lying in the preauditory region that might be mistaken 

 for primordia of sensory lines. 



Froriep ('85) described in mammals what he called '^Anlagen 

 of sense organs" on the facialis, glossopharyngeus and vagus and 

 thought that their relationship placed them with the lateral line 

 system. When we recall the fact that lateral lines are not pres- 

 ent in mammals and find that the structures he figures and de- 

 scribes as ''sense-organ Anlagen" lie just above the gill clefts, 

 we assume that they were in reality the epibranchial placodes. 



Beard ('85 '88) confirmed the observations of Froriep and de- 

 scribed similar epidermal thickenings in reptiles, birds, teleosts 

 and elasmobranchs, and like Froriep thought they were related 

 to the lateral nerves. He introduced the term ''branchial sense 

 organs" for these primordia which may have been primordia of 

 the lateral line but seem, in most if not all cases, to have been 

 epibranchial placodes, on account of the relation to the gill 

 shts which he attributes to them. He failed, however, to make 

 a clear distinction between dorso-lateral and ventro-lateral 

 placodes, as von Kupffer ('91) points out, nor can we find in 

 Beard's writings a consistent distinction between the dorso-lateral 

 placodes and the early stages of the lateral line organs. The 

 distinction between dorso-lateral placodes and ventro-lateral or 

 epibranchial placodes is clearly stated by von Kupffer ('91) and 

 he seems clear as to the relation of the epibranchial placodes to 

 the visceral ganglia, rather than to the so-called lateral nerves. 



The work of Froriep and Beard throws little light on the prob- 

 lem of this paper further than to make it clear that there are 



