LATERAL CANAL SYSTEM OF SELACHIANS 3 



70) extended this to organs of the lateral line of the trunk of 

 teleosts and amphibians. No earlier author had reached this 

 conclusion, for the conclusions of Jacobson and of Savi applied 

 only to particular organs of restricted range, while Leydig's 

 and Schulze's were for the first time applied to the widely dis- 

 tributed lateral line organs common to fishes and to amphibians 

 in their aquatic stages. 



Since 1870 morphological studies of the lateral line system of 

 fishes have taken two directions: (1) more extensive studies of 

 topography including the anatomical pattern, the nerve supply, 

 the comparative distribution and (2) studies of histology and 

 embryology. It is in the second division named that investiga- 

 tion is most needed. While advances have been made in other 

 directions, little progress has been made in reference to histo- 

 logical detail. The embryonic development is also imperfectly 

 known except in its more general features. The method of 

 growth of the sense organs, the formation of the canals, the posi- 

 tion of the neuroblasts, the nature of the peripheral termina- 

 tions of nerve fibers and the histological structure of the sense 

 organs remain in doubt. 



It was with the hope of adding something to this phase of the 

 subject that the investigation reported below was undertaken. 

 The observations cover the period from September, 1914, to 

 June, 1916, and were carried on in the zoological laboratory of 

 Northwestern University under the supervision of Prof. William 

 A. Locy, to whom grateful acknowledgment is accorded for 

 inspiration and pertinent criticism. 



II. BRIEF COMMENTS ON THE LITERATURE 



The literature on the canal system prior to 1850 is of little 

 importance from the morphological point of view. The two 

 papers of Steno^ describing the distribution of supposed mucous 

 pores on the head of the skate (1664) and of the shark (1667) 



- Regarding his name, Steno is the form commonly adopted at the present 

 time, but the Latinized, Stenonis, was generally used by its owner rather than 

 the Danish form, Steensen. 



