TYPE TRACHEATA. 497 



appearance from the males, and in man}- Beetles the male is 

 adorned with spines and tubercles upon the head which are 

 but rudimentary or absent in the female. Differences in the 

 shape of the antennae and the presence or absence of stridu- 

 lating organs also serve to distinguish the two sexes in some 

 of the groups. In a few forms a polymorphism is produced 

 by the failure of certain individuals to reach sexual maturity 

 and by the assumption by them of certain special structural 

 characteristics. Examples of such cases are afforded by the 

 Bees, Ants, and Termites, the workers of the first two groups 

 being immature females, w r hile in the Termites (Fig. 237) the 

 so-called neuters may be either males or females, always, 

 however, immature. 



The ovaries (Fig. 227, ov} are paired and consist of a 

 varying but usually rather large number of tubes, which start 

 from a common basis. At the extremit}- of each tube is the 

 germ-producing region, the rest of the tube being divided into 

 a series of chambers each of which contains an ovum sur- 

 rounded by a layer of follicle-cells. Not uufrequeutly the 

 chambers are arranged more or less distinctly in pairs, the 

 lower one of each pair containing an ovum, while the upper 

 contains a number of small cells similar in appearance to the 

 primary germ-cells, but which serve as nutrition for the ovum 

 which gradually absorbs them (see Fig. 20). From each 

 ovary an oviduct arises, the two, however, soon uniting, and 

 receiving, usually not far from the unpaired orifice, the ducts 

 of various glands (ag) whose secretion serves to cause an 

 adhesion of the ova to the structures on which they are 

 deposited. A receptaculum semiuis is usually present, and 

 there is frequently a large pouch, partially separated from the 

 oviducts, which receives the male organ during copulation and 

 is termed the bursa copulatrix (be). The genital orifice is situ- 

 ated on the ventral surface of the ninth abdominal segment 

 and is usually surrounded by a number of papillae, or some- 

 times by long processes, which serve as ovipositors and are 

 to be regarded simply as processes of the segments from which 

 they arise and not as modified limbs. 



The testes are also paired, each being composed of a 

 number of separate spherical or tubular portions. The ducts 



