176 PEABODY. [VOL. I. 



In the lateral-line system of the same selachians there is a 

 decreasing complexity observed in the animals less active in 

 their habits. Galeus has a much-branched, dendritic system 

 of tubules; in Raja the tubules are almost entirely simple, run- 

 ning in a direct course from the lateral-line canal to the surface 

 pores; in Torpedo the same simple plan is observed on the 

 dorsal surface, while on the ventral surface of the fish the lat- 

 eral-line canal system has wholly disappeared, its place being 

 taken, according to some writers (Garman, '88, Fritsch, '90), by 

 Savi's vesicles. 



Whether this simplicity of structure of lateral-line and 

 ampullary organs is always correlated with sluggishness of 

 habit is a question which can only be answered by a careful 

 study of many different genera of the selachians. 



Attention should be called, in the discussion of the glandular 

 theory of the ampullae, to the fact that in Galeus, where the 

 ampullae are most numerous, the skin is free from slime, 

 while in the skate the slime is very abundant. It is highly 

 improbable, therefore, that this slime is produced in the 

 ampullae. On the other hand, an increase of sensory func- 

 tion would be expected to accompany a wider range of body 

 movement. 



Some experiments in cutting the nerves and studying the 

 effect on the ampullae have been begun which may throw some 

 light on the physiology of these organs. But at the present 

 time no hypothesis yet suggested seems to me to explain the 

 function of the ampullae in the economy of the life of the 

 selachians. 



My work on the ampullae of Lorenzini of the selachians 

 was begun at the Marine Biological Laboratory at Woods Holl, 

 Mass., in the summer of 1892. The original object of this 

 research, as suggested by Dr. Howard Ayers, was to determine 

 the relation (whether of contact or continuity) which exists 

 between the nerve fibers and the cells of this so-called sense 

 organ. The methylene blue stain seems to have given decisive 

 evidence on that point. The problem has, however, gradually 

 assumed a larger interest from the standpoint of comparative 

 anatomy and physiology. 



