20 EVENINGS AT THE MICKOSCOPE. 



furrows, across wliicli, contrary to tlie ordinary rule, the 

 close-set concentric lines that follow the sinuosities of 

 the outline are not visible. Under the microscope they 

 look as if they had been split in these radiating lines, 

 after the whole number of layers had been completed, 

 and the fissures had then been filled with new trans- 

 parent substance. 



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 

 tlie other scales, and are pierced by a tubular orifice for 

 the escape (as is generally 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 protecting the skm from the mas- 

 cerating influence of the surrounding water, and of di- 

 minishing 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 ai-e of this description. Tliis dead Gold-fish shall 

 give us examples. The three scales in the upper row 

 are from the lateral line, the left-hand one («) taken just 

 behind the head, the second (J) near the middle of the 

 body, and the right-hand one (<?) near the tail. Of the 

 lower row, the first {d) is from the back, the second («?) 

 from the middle of the belly, and the last (/) from the 

 throat. Thus we see there is considerable variety in 

 form presented by the scales even of the same individ- 

 ual fish. They all, however, difler from those of the 

 Perch, in this respect; — that their free overlapping 

 edges are entire, or destitute of the crystalline points 

 udiich we saw in the former examples ; while thoy agree 



