18 IN SECT A. 



moves freely upon the second abdominal ring. On 

 the ventral side there is no corresponding part to 

 represent the sternum. On each side of the abdomen 

 the skin is turned inward, forming a longitudinal fold 

 (PL L, Fig. 7, /) which separates the upper part of 

 each ring from the lower. Just above this fold, on 

 either side, is a row of breathing-holes, or spiracles 

 (Fig. 7, /-j-^"). Each spiracle is a slit-like opening 

 surrounded by a horny ring, and is situated on the 

 anterior portion of the segment : these will be referred 

 to again under the respiratory system (see p. 2>^^' 



The abdomen of the male (PI. I., Fig. 7, C) is simpler 

 in structure than that of the female. The first eight rings 

 (Fig. 7, c^-c^) can be readily counted, while the ninth and 

 tenth (PI. I., Fig. 8, ^^ c^^^ are fused together, the suture 

 showing on the median line, but not extending on either 

 side so far as the fold (Fig. 7, siit^. The corresponding 

 space on the ventral side is occupied by the sternum of 

 the ninth ring (Fig. 7, >^^), which is broader than the sterna 

 of the other segments and without any visible suture. Be- 

 hind the ninth abdominal sternum is the subgenital plate 

 (Fig. 7, >^^). In the female the sternum of the eighth 

 ring (PI. I., Fig. 9. k"") extends backward to form the sub- 

 genital plate, which terminates in the egg-guide {^eg. ; see 

 also Fig. 14, egg-guide). Attached to the tenth ring is the 

 shield-shaped piece (PI. I., Figs. 8, 9, ;/), which embry- 

 ology proves to be the tergum of an eleventh segment : 

 Fig. 9, ;/' is the tip of the tergum. On either side of the 

 tergum are the podical plates (Figs. 8, 9, ^), and between 

 these is the anus. Lying upon the podical plates, and 

 fastened to the tenth segment, are the movable cerci 

 (Figs. 8, 9, /), which are not true appendages. At the 

 extreme end of the abdomen are parts connected with the 

 genitalia, which will be described in their proper place 

 (see p. 33). 



