32 



EVENINGS AT THE MICROSCOPE 



The middle scale is, as I have said, from the lateral line. 

 Along each side, in most fishes, may be observed a line, 

 known as the lateral line, formed by scales of peculiar form. 

 They are commonly more bony than the other scales, and 

 are pierced by a tubular orifice for the escape (as is gener- 

 ally supposed, though this has been denied) of a mucous 

 secretion, which is poured out from glands beneath, and 

 thus flows over the body for the double purpose of pro- 



SCALES OF GOLD-FISH. 



tecting the skin from the macerating influence of the sur- 

 rounding water, and of diminishing friction in swimming. 

 Let us now look at some scales of the cycloid kind. The 

 great majority of our fishes are clothed with such as are of 

 this description. This dead Gold-fish shall give us exam- 

 ples. The three scales in the upper row are from the lateral 

 line, the left-hand one (a) taken just behind the head, the 

 second (b) near the middle of the body, and the right-hand 

 one (c) near the tail. Of the lower row, the first (d) is from 

 the back, the second (e) from the middle of the belly, and 



