CHEMORECEPTION: LOCOMOTION AND ORIENTATION 



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The supporting cells surrounding the receptors are high, narrow, and cylin- 

 drical. Their distal ends carry microvilli in various numbers and lengths and, 

 in a number of species (including fish), cilia (Langerhans 1876; Watling and 

 Hillemann 1964). In a number of vertebrates these cells actively secrete 

 granules when strong olfactory stimuli are applied (Bloom 1954; Bronshtein 

 and Tvenov 1965; Reese 1965; Frisch 1967; Graziadei 1971). The phenom- 

 enon, whose functional significance is unknown, has been described in many 

 vertebrates and may be assumed to occur also in elasmobranchs. It has 

 already been mentioned that adjacent supporting cells are in close contact 

 with each other, particularly near their distal ends, through the array of 

 junctions that form a belt encircling each cell (Graziadei 1971; Reese and 

 Brightman 1970). 



Although Bowman's glands, abundant in the olfactory epitheliums of 

 mammals, are absent in fishes, mucus glands have occasionally been de- 

 scribed in these animals, including Mustelus canis (Asai 1913). In this 

 species, mucus-secreting goblet cells are located in the lamellae. These cells 

 reach the epithelial surface through an extension that compresses the neigh- 

 boring cylindrical cells (Figure 6). 



Figure 6 Mustelus canis mucus cell (A) in the indifferent epithelium of the free surface 

 of a lamella, in which it compresses the neighboring cylindrical cells (B). From Asai 

 (1913). 



