THE MALE ORNEBATIVE OBGANS. 101 



also at the posterior extremity of the abdomen in the vicinity 

 of the ovipositor in the female, and around the testes in the 

 male. A small pair exist behind the optic nerves, and a second 

 but still smaller pair may be observed adhering to the posterior 

 cornua of the pharynx. 



They consist of arborescent follicles (Plate IX., figs. 2, 2a, & 

 2b), which adhere to the tracheal trunks which supply them. 

 The follicles are very transparent and structureless, but are 

 largely supplied with minute tracheal vessels. In the young 

 fly, they only contain nucleated cells, l-3000th of an inch in 

 diameter, free nuclei, and molecular matter ; but later in the 

 life of the insect they become loaded also with oil globules and 

 granular cells, especially in the female, sometimes to such an 

 extent that the abdomen becomes distended as if with mature 

 ova ; this fat disappears as the ova are developed. 



A pair o folliculate glands* (Plate IX., fig. 3) are found in 

 the larva, one on either side of the dorsal vessel ; each follicle 

 contains one or two nuclei or nucleated cells. When the larva 

 arrives at maturity they become filled with granular matter, 

 and undergo disintegration before the formation of the pupa 



Section XX. The Male Generative Organs. 

 PLATE IX. 



The male organs (Plate IX., fig. 5) are a pair of testes 

 with their ducts, and a pair of albumen glands, which open with 



* Zellenstrangen, Weismann. 



