212 



HISTOLOGY 



ments of the second pair of wings developed into the so-called " balancers." 

 The writers have found by experiment, however, that flies can fly as 

 well without these organs as. with them. Insects certainly cannot use 

 sight to maintain their static equilibrium. Most of them cannot see far 

 enough or well enough to do this. And even when blinded or in dark- 

 ness, the static sense is not gone. Their activities would also demand 

 a spatial sense, and yet evidences of structures used for this purpose have 

 not been found. 



The static tissues of the vertebrates have been complicated by the 

 specialization of parts of their static epithelia to hear sound, as is de- 



8t.C. 



FIG. 192. Part of a longitudinal section of an ampulla from the skate, Raja lavis, showing a 

 transverse section of the sensory epithelium on the medium septum, gen.ep., general epi- 

 thelium composed of static cells (st.c.) and supporting cells, sen. ep., sensory epithelium. 

 A nerve fiber can be seen entering the epithelium and dividing. 



scribed in another part of this chapter. We shall study the sensory 

 epithelium found in the ampullae of the semicircular canals as probable 

 examples of tissues which perceive the spatial movements of the body, 

 or of the head when that part is moved independently. The origin and 

 general relations of the semicircular canals have been indicated in 

 another part. We may repeat here that they are integral parts of the 

 statocyst cavity and that one end of each, where it joins the utriculus, 

 is enlarged in diameter to form an ampulla of which there are three, one 

 for each canal. This ampulla contains an oval cavity, in the fish which 

 our figure represents, and the lining epithelium covers the entire interior 

 of this cavity, including a ridge rising across its middle at right angles 

 to the length of the lumen. This ridge rises almost exactly halfway up, 



