136 



VIEWS OF THE MICROSCOPIC WORLD. 



Fig. 229. 



It is a beautiful scale, resembling a shield in form, 

 and the entire surface is covered with numer- 

 ous radial lines crossing the concentric strata. 



A scale of the roach is exhibited of its na- 

 tural size in figure 230, and the same magnified 

 | is shown in figure 231. It is seen to differ 

 from all the preceding scales in many particu- 

 lars. The broad flutings rise fan-shaped from 

 [the centre of the scale, flanked on either side by 

 numerous concentric lines, which indicate the 

 position of the edges of the overlapping strata. 

 These lines do not terminate at the extreme ra- 

 dial branches, but pass across them as in the case 

 of the parrot-fish. The lower portion of the 

 figure, which is apparently covered with teeth, 

 represents the root of the scale, by which the 

 latter is attached to the fish. The distance, a, 

 b, between two of the radial lines, as measured 

 by the micrometer, is one- fiftieth part of an 

 inch. 



^ n % ure 232 an( ^ 233, an ther scale is shown, 

 kth * n * ts rea ^ anc ^ ma o mne d dimensions. It is 

 fo Q SC ale of the flounder, and resembles in some 

 points that of the roach. The series of concentric 

 lines on each side, crossing the radial divisions, are mainly alike, and the fan-like 

 flutings are seen in both, only their divergence is far greater in the scale of the 

 roach than in that of the flounder. Owing to this circumstance the forms of 

 the scales are different, that of the roach being broader than it is long while in 

 the case of the flounder, the length exceeds the breadth. The distance between 

 two of the radical lines, a and 6, in figure 233, is the one-three hundred and 

 tenth part of an inch. 



Figure 234 is a magnified portion of the skin of a sole-fish, viewed by re- 

 flected light the dark ground representing the skin, and the lighter parts the 

 upper protruding portions of the scales, which exhibit a beautifully serrated ap- 

 pearance. Figure 235 is the same, of its natural size. 



THE INTERNAL ORGANS OF RESPIRATION OF THE SILK- WORM. The mode in 

 which insects respire, is very different from that which exists among the higher or- 

 ders of animals. They are not possessed of lungs, neither do they breathe through 

 the mouth ; but inhale the air through numerous orifices, called spiracles, with 

 which are connected respiratory tubes, that extend in minute ramifications to every 

 part of the body. These tubes, which are divided into two classes, consist of 

 three coatings. The first, or external envelope, is a membrane comparatively 

 thick, strengthened by a great number of fibres, which fornj around it numer- 



Fig. 228. 



