358 F. L. LAND ACRE 



are innervated from ganglia derived from the lateral mass or 

 neural crest of other types while those posterior to the ear are 

 innervated partly by ganglia derived from the auditory vesicle 

 and partly by ganglia derived from the posterior extension of the 

 vesicle or the postauditory placode. 



The foregoing description of the relations existing between the 

 pre- and postauditory placodes and the lateral line organs, differs 

 so much from that of Wilson ('91, '97) in the sea bass and salmon 

 that it merits a fuller discussion. The accounts differ as to the 

 mode of origin of the lateral line organs, Wilson tracing them to 

 the sensory lines derived from the postauditory placode and the 

 preauditory placode (branchial sense organ of Wilson and Beard) 

 while the present account traces them to differentiations of the 

 epidermis not derived from the placodes. Wilson's statement of 

 the case as given in his short paper on the salmon ('97) is as fol- 

 lows and will stand for the conception of those authors who agree 

 with him. He states that in Serranus 



The organs of the lateral line, the auditory sac, and the superficial sense 

 organs of the head (presumably all) were derived from a common founda- 

 tion. This common foundation has the shape of a long furrow (ecto- 

 derrnic) on the side of the head region. The furrow splits into three 

 parts, the posterior part giving rise by division to the organs of the lat- 

 eral line, the middle part becoming the auditor}- sac, the anterior part 

 becoming a histologically developed branchial sense organ, situated in 

 front of the single gill slit of the embryo, from which a (sensory) cord of 

 cells is prolonged forwards. 



Wilson finds practically the same condition in the salmon except 

 that the pre- and postauditory furrows are only thickenings in 

 this form, and cites Mitrophanow f 93) and Locy ('95) as agreeing 

 substantially with him. 



The paper on the salmon is brief and does not describe the exact 

 mode of appearance of the definitive lateral line organs. An ex- 

 amination of Wilson's paper on the sea bass ('91) shows that the 

 relation of the preauditory lateral line organs to the preauditory 

 placode is much less definite than in the paper on the salmon. He 



