163 



ganglion is always associated with the trigeminus, except 

 in the Physostomi, where there are no ganglia in front of 

 the vagus. This is what we should expect, as the cranial 

 sympathetic appears for the first time in the bony fishes, 

 and the Physostomi are undoubtedly a primitive group 

 of Teleosts. 



F.— THE SENSE ORGANS. 



1. — The System of Lateral Sense Organs 

 OR Sensory Canals. 



(Figs. 23 and 29.) 



The obvious line seen at the side of the body in most 

 Fishes, including the Plaice, and known as the lateral 

 line (Seitencanal of German authors), is in our type a 

 long tube or lateral canal, protected by a row of modified 

 scales (lateral line ossicles), and opening on to the surface 

 by pores at more or less regular intervals. These pores 

 may open directly into the canal or they may do so by the 

 intermediation of a little tubule. At first the only sub- 

 stance found in such a canal as this was a quantity of a 

 jelly-like mucus, and hence these canals were called 

 mucous canals, and were supposed to secrete the mucus 

 on the surface of the body. The discovery, however, that 

 they contained large sense organs, one of which usually 

 occurred between two succeeding surface pores, and thaii 

 the mucus was only of minor importance, and developed 

 by the numerous goblet cells in the lateral canal itself to 

 enable the sense organs to perform their function, and also 

 that the mucus in the lateral canal was of quite a difPerent 

 character to that occurring on the surface of the body, 

 conclusively proved that these lateral canals constituted a 

 sensory structure and could not therefore be called mucous 



