INTRODUCTION. 5 



of seven segments, if the hypopygium be considered as a single 

 segment ; of the sixth segment only the upper half is distinctly 

 developed, but it is much narrower and shorter than the surface 

 of the immediately preceding segments. When this sixth segment 

 is concealed under the upper half of the fifth, or when it is strik- 

 ingly different by its coloring from the preceding segments and 

 resembles in this respect the seventh, then the male abdomen 

 appears only five-jointed. The seventh segment consists of the 

 proportionally large hypopygium, the structure of which, near its 

 basis, is not quite symmetrical. It consists of a rather stalk-like 

 basal part and of a club-shaped posterior part ; the stalk-like part 

 is often very much abbreviated, and then not easily perceptible ; 

 the club-shaped part is movable towards it ; the junction of both 

 parts lies always above, on the left hand side of the club-shaped 

 portion. 



The hypopygium is more or less inflected under the abdomen, 

 sometimes imbedded in an excavation of the venter proportionate 

 to its size. At the tip of the inflected hypopygium, below, are 

 inserted, by means of articulations, three pairs of appendages of 

 manifold structure. The outer pair of these appendages is gene- 

 rally larger than the two others, and must be considered as organs 

 of a great irritability, as the roots of the hairs on their inside are 

 connected with nerves. The basis of this pair is linked to the 

 hypopygium by a free articulation. The two other pairs, attached 

 by a less free articulation, can be considered as organs for the 

 purpose of seizing, clutching ; they lie within the former pair and 

 are not seldom of a very complicated structure. Sometimes one 

 or the other of these pairs exceeds in length the outer pair. In- 

 nermost between them, coinciding with the middle line of the 

 clutching apparatus, a single appendage is inserted, which also 

 appears to be linked at its basis. On the upper side of the hypo- 

 pygium, which is the side turned towards the abdomen, there are 

 two more appendages, usually in the shape of a gutter ; they have 

 no link at their insertion. Above this gutter, or, more seldom, 

 within it, is another appendage, in the shape of a spike, which in 

 some cases is somewhat button-shaped at the tip ; it is pierced 

 lengthwise by a channel, and incloses more or less completely the 

 penig, which protrudes considerably during the act of copulation. 

 This organization is most distinctly developed in the genus Doli- 

 chopus, whereas it is more difficult to observe in the genera with 



