1918] Morphology of Genitalia of Insects 121 



The genital opening of the male is connected with the tenth 

 sternite more closely than with any other, as Berlese states. 

 However, certainly in the adult insect, it is also situated at the 

 distal end of an intromittent organ, which is, in many cases 

 when entirely protruded, nearly as long as the abdomen, and 

 thus the ejaculatory duct is also prolonged to an equally great 

 length, therefore, bringing the external opening itself to a point 

 without any relation to the abdominal sclerites. 



Somewhat similar cases occur in such females as possess long 

 ovipositors. However, the distal opening of the vagina itself is 

 seldom situated far beyond the bases of the ovipositors. When 

 the eggs leave this opening, they follow along well-marked 

 grooves on the inner surfaces of the ovipositors into the ground, 

 stem, or other object in which they are to be laid. This same 

 mechanism may exist for the exit of poisonous fluids exuded at 

 the bases of stings, or, as is often the case, through excurrent 

 ducts leading from the glands to an external opening, or paired 

 openings, also situated at the bases of the stings. 



In those insects which have their caudal segments and gen- 

 itaHa retracted, the caudal end of the body has a smoothly 

 rounded contour, or it may even be pointed. Excellent exam- 

 ples of such cases are seen in the Diptera and Hymenoptera. 

 In these, one is unable to identify the sex from the genitaha 

 unless they are extruded, but one must instead use other char- 

 acteristics varying in the two sexes — those commonly called 

 secondary sexual characters. Those abdomens which terminate 

 with most of their distal segments and appendages in view, 

 show projections of a tactile, clasping, or other function, and, 

 although usually bilateral in arrangement, they are very irreg- 

 ular in appearance by contrast with those smooth forms 

 described above. Here, of course, it is very often possible to tell 

 the sex easily from the genitalia alone. 



The anus is always surrounded by cuticular membrane 

 divided into folds generally called anal lobes. It is often difficult 

 to decide upon the number of the distal segment in adult insects 

 because it cannot be difTerentiated from this membrane which 

 may very well be made up, morphologically, of more than 

 one segment. 



In numbering the segments of this region it is not necessary 

 to begin with the first abdominal one. The most caudal pair of 



