210 THE INTEGUMENTAL SKELETON OF THE IMAGO. 



seventh segment in the male, and a second pair lie one on each 

 side of the dorsal plate of the ninth segment ; but neither pair 

 is segmented in the Diptera. 



In the female a single pair of leaf-like appendages exist at 

 the end of the ovipositor on the ventral surface of the triangular 

 dorsal plate of the ninth segment. 



b. The Abdominal Skeleton of the Blow-fly. 



Eight distinct annuli are present in both sexes, with a tri- 

 angular dorsal plate, the epipygium, representing the ninth in 

 the female. The epipygium is a deeply-cleft style-like organ in 

 the male. 



The five anterior annuli form a pyriform capsule in both 

 sexes, each overlapping the one behind it, so as to protect the 

 soft syndesmotic membrane uniting them ; the remainder are 

 invaginated within the fifth. These form a cloaca in the male 

 and a long ovipositor in the female, the sixth, seventh, and 

 eighth segments being drawn one within the other when the 

 organ is at rest. 



The first abdominal annulus is very narrow, and its external 

 surface looks forward ; so that it is almost entirely concealed by 

 the thorax. Its dorsal arch terminates below in narrow points 

 behind the short, broad ventral plate, so that the syndesmosis 

 between the dorsal and ventral plates is nearly vertical. This 

 syndesmosis contains the first pair of abdominal spiracles. 



The second annulus is the largest of all. The lateral por- 

 tions of the dorsal arch are rectangular, and have the second 

 abdominal spiracles near their anterior angles. The ventral 

 plate of this segment is subquadrate. 



The third, fourth, and 'fifth segments are very similar. The 

 ventral plates become shorter from the second to the fifth. 

 The posterior margins of the fourth, fifth, and sixth segments 

 are fringed with strong curved bristles. 



In the male the ventral plate of the fifth segment is deeply 

 incised by a Y-shaped cleft, the edges of which are united by 

 syndesmotic integuments. This arrangement permits of the 



