226 LECTURE XVIII. 



circular indentation and by the two distinct vasa deferentia. In 

 certain moths, as the Tiiiea, the original condition is retained in the 

 imago state. The vasa deferentia and tubular glands are extremely 

 long and convoluted tubes. 



In the male Aphis three, four, or five spherical testes communicate 

 by short tubes with a common transverse duct, the two extremities of 

 which bend down and complete the circle by uniting to form the short 

 ductus ejaculatorius. A long pyriform vesicular gland is appended 

 to each lateral vas deferens. 



In all other insects the testes form a pair of white glandular 

 bodies : in the dragon-fly they are elongated and fusiform, as in the 

 Centipede. In the Cercopis each testis is a clavate gland, gradually 

 contracting to the vas deferens. In the crane-fly ( Tipula) the testis 

 is a convoluted filamentary tube, dilating into a vesicle before it is 

 continued into the vas deferens : in the Ranatra the tube is twisted 

 spirally. In the Dytiscus the testis is a filiform tube, much longer 

 than the abdomen, but convoluted into a round ball. In the Hydro- 

 philus, a series of short blind processes are given off from one side of 

 a common duct. In the Buprestis a fasciculus of longer caecal tubes 

 radiate from the end of the sperm duct. Sometimes the extremities 

 of similar radiating tubes are dilated into saccular flattened glands, 

 as in the rose-beetle {Cetonia), and numerous more composite forms 

 have been detected ; all, however, are referable to modifications of 

 the primitive blind secerning sac. Their analogy to the sexual parts 

 of plants has already been alluded to, and Entomologists have found 

 it requisite or advantageous to borrow the neat and descriptive terms, 

 with which Linnaeus has enriched botanical science, in order to indi- 

 cate the diversified forms of the male apparatus. 



The vasa deferentia always receive the ducts of glands which are 

 analogous to the vesiculse seminales ; these are generally formed of 

 slender tubes, not exceeding the length of the abdomen in the 

 Lucanus, Locusta^ and Libellula, but five times longer than the body 

 and much convoluted in Dytiscus, ten times as long as the body in 

 Blaps, and thirty times as long in the Cetonia aurata. The sperm- 

 duct is dilated where it receives the secretion of the accessory glands, 

 as in the bee. In many insects,, representatives of prostatic glands 

 communicate with the ductus ejaculatorius. 



The intromittent organ is a modification of the last or two last 

 segments of the abdomen, and is usually retracted out of sight : it 

 consists of a large exterior sheath and a delicate membranous tube : 

 the sheath commonly consists of two lateral valves. Accessory pre- 

 hensile organs are developed in some insects, of which the most 

 remarkable are attached to the base of the abdomen in the male 

 Libellula. 



