MECHANORECEPTORS AND BEHAVIOR 



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arrangement in rays differs considerably from that of sharks, particularly in 

 the length of the hyomandibular canal, although most writers would accept 

 Garman's view that the batoid configuration could be transformed from the 

 shark arrangement, if the starting form was a fish like Chlamydoselachus. In 

 other species, like Pristiurus with its elongate snout or Sphyrna with its 

 bizarre head, the normal pattern is of course distorted, while in bottom- 

 dwelling species like Raja the ventral canals have few openings (Figure 7C) or 

 are absent (Torpedo); these canals are well formed and have extensively 

 dichotomizing tubules in open-ocean rays such as Myliobatis (Figure 7D). 



Histology of the canal system— Although tubules and canals are both 

 lined with two-layered epithelium, only in the canal, where the dorsal wall is 

 modified to form an almost continuous sensory epithelium, are neuromasts 

 to be found (Figure 8). 









Figure 8 

 showing 

 (arrow). 



Light micrograph of a transverse section through the body wall of Scyliorhinus, 

 the lateral-line canal lined with an epithelium that is swollen at the neuromast 



The centre of each neuromast, decked by its own cupula, lies opposite an 

 opening of a tubule so that, except where this branches, the number of 

 neuromasts is equal to the number of pores. This number differs among 

 species even for the same canal; thus the infraorbital canal of Mustelus 

 contains 110 organs (Allis 1901) but that of Chlamydoselachus only 52 

 (Hawkes 1906). The organization of the canal epithelium has been well 

 described at the level of the light microscope for Mustelus by Johnson (1917) 

 and for Carcharhinus by Tester and Kendall (1969), while the ultrastructure 

 of the cells is outlined by Roberts and Ryan (1971) and Hama and Yamada 

 (1977). 



