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



gans of the main body line. These organs are all supplied by the 

 ramus lateralis X. Whether the accessory organs found later 

 lying above the main lateral line arise by splitting off from that 

 line could not be determined. These are supplied, however, 

 from the same ramus. The relations of this third primordium 

 to the lateralis X ganglion are quite similar to those of the two 

 more anterior to their respective ganglia. The posterior end of 

 the ganglion comes so close to the lateral line primordium as to 

 suggest its derivation from that primordium, but here again our 

 series are not close enough together to settle the question. 



The third primordium, as in the case of the other two, is more 

 dorsal in position than the gill thickenings and quite distinct 

 from them, although at the time of its appearance its posterior 

 end drops to the level of the gill thickenings. This is, however, 

 at a point back of the region in which the last .gill thickening 

 appears. 



The definite mode of appearance of the postauditory lateral 

 line primordia, the absence of a postauditory placode, and es- 

 pecially the presence of a number of gill thickenings which might 

 easily be mistaken for either of the two preceding thickenings, 

 but whose history has been traced, furnish positive evidence 

 against the theory that the lateral line primordia are derived 

 genetically from the auditory vesicle. 



LITERATURE CITED 



Allis, E. p. Jr. 1889 The anatomy and development of the lateral line system 

 in Amia calva. Jour. Morph., vol. 2, no. 3. 



Ayers, H. 1892 I. Vertebrate cephalogenesis. II. Contribution to the mor- 

 phology of the vertebrate ear, with a reconsideration of its functions. 

 Jour. Morph., vol. 6, nos. 1 and 2. 



Beard, J. 1885 The system of branchial sense organs and their associated 

 ganglia in Ichthyopsida. A contribution to the ancestral history of 

 vertebrates. Quart. Jour. Micr. Sci., vol. 26, pp. 95-156. 

 1888 Morphological studies. II. The development of the peripheral 

 nervous system of vertebrates. Part II. Elasmobranchii and Aves. 

 Quart. Jour. Micr. Sci., vol. 29, no. 114. 



Beckwith, Cora J. 1907 The early development of the lateral line system of 

 Amia calva. Biol. Bull., vol. 14, December, pp. 23-28. 



