72 SYDNEY EVANS JOHNSON 



mass fibers grow out from the cells of the latter and become as- 

 sociated with, the overlying ectodermal cells. Very early in 

 development a longitudinal mass of the gangUonic cells becomes 

 partly separated from the rest. This is the embryonic laterahs 

 ganglion. Its central fibers form a definite root which enters 

 the medulla anterior to, and slightly above, the roots of the 

 remainder of the ganglionic (vagus) mass. Peripheral fibers 

 of the laterahs ganglion have ah-eady become associated "svith 

 the ectodermal cells which proliferate and extend backward as 

 the lateral sensory cord. The fibers which accompany the 

 sensory cord constitute the laterahs nerve. In early embryos 

 the nerve hes immediately subjacent to the sensory cord, but 

 as growth proceeds it recedes from the surface and comes to 

 occupy a position at a considerable depth medial to the ecto- 

 derm. As the nerve becomes farther removed from the inner 

 surface of the ectoderm the fibers, which have become associated 

 with the sensory cord, do not pass to the latter in a continuous 

 sheet, but arrange themselves into small bundles, the lateral 

 ramuli. 



Mode of formation of the canals. By the time the nerve con- 

 nections are established as outlined above the canals are closed 

 and the sensory canal system has practically reached the adult 

 condition. 



VI. BIBLIOGRAPHY 



Allis, E. p. 1888 The anatomy and development of the lateral line system in 



Amia calva. Jour. Morph., vol. 2. 



1902 The lateral sensory canals, the eye-muscles and the peripheral 



distribution of certain cranial nerves of Mustelus canis. Q. J. M. S., 



vol. 45. 

 Balfour, F. M. 1878 The development of elasmobranch fishes. 

 Beard, John 1884 On the segmental sense-organs of the lateral line and the 



morphology of the vertebrate auditory organ. Zool. Anz., Bd. 7. 

 BoDENSTEiN, Emil 1882 Der Seitenkanal von Cottus gobio. Zeit. f. wiss. 



Zool., Bd. 37. 

 Bunker, F. S. 1897 On the structure of the sensory organs of the lateral line 



of Ameiurus nebulosus. Anat. Anz., Bd. 13. 

 Clapp, C. M. 1898 The lateral line system of Batrachus tau. Jour. Morph., 



vol. 15. 

 Cole, F. J. 1895 On the cranial nerves of Chimaera monstrosa with a discus- 

 sion of the lateral line system, etc. Trans. Royal Soc. of Edinb., 



vol. 38, part 3. 



