120 EVENINGS AT THE MICROSCOPE. 



segments to the abdomen ; at the eighth it seems to 

 divide into two branches, one longer than the other. 

 This appearance, however, is due to the circumstance 

 that the respiratory tube is sent forth from the eighth 

 segment, and that the ninth and tenth segments are 

 bent away at an angle from the general line of the 

 body. 



The ninth segment is very small : the tenth is squar- 

 ish, with rounded corners, and is brought to a thin 

 edge. Around the margin there is the most exquisite 

 array of hairs possible ; at one corner there are three 

 pencils ; while round the opposite, and down the cor- 

 responding side, run in two rows twelve pencils, set 

 very close to each other, and each containing a large 

 number of very slender hairs. The extreme end of the 

 segment is ornamented with four diverging organs of 

 taper conical form and crystalline clearness, through 

 the midst of each of which passes a very fine branch of 

 the air-tube system, which gives off still more at- 

 tenuated branchlets in its course. 



We have not yet, however, examined the origin 

 of this air-breathing system. There is but one en- 

 trance to the air, or rather two placed close together, 

 at the end of that round column, which is sent off from 

 the eighth segment of the abdomen. This column, 

 which is roughened all over with minute points, and 

 fringed with rows of hairs, ends in a horny, conical 

 point, which seems entire while under water, but no 

 sooner does it come to the surface, than it is seen to 

 oplit into five triangular pieces, which open widely, and 

 expose a hollow, at the bottom of which are the two 

 spiracles. 



From these the two main air-pipes are seen to con) 



