GENERATION OF INSECTS. 397 



into a sperm-reservoir. The accessory prostatic glands are bent 

 upon themselves, like a common magnet ; one end of each opens into 

 the ductus ejaculatorius. 



In the order Diptera the testes always present themselves as two 

 simple glands, either pyriform, oval, or elongated and twisted, the 

 outer capsule of which is of a brown or yellow colour ; in the 

 Asilus, when this outer coat is removed, the surface of the testis is 

 nodulated by the prominent ends of the component caeca ; two 

 slender sperm-ducts terminate in a small sperm receptacle, which 

 also receives two long filamentary prostatic glands ; a long ductus 

 communis is then continued to the base of a trifid penis.* 



In many of the Lepidoptera the testis is clothed with bright pig- 

 ment, crimson in the common white butterfly {Pontia hrassiccB\ 

 and green in the Sphinx. In most of the species the two glands 

 approximate, and become confluent in the progress of the meta- 

 morphosis \\ but in certain moths, as, e. g., the Tinea, the originally 

 distinct condition of the testes is retained in the imago state ; the 

 testes also remain distinct in the Yponomeuta. % In most Lepidoptera 

 the vasa deferentia, or sperm-ducts, after a short course, receive two 

 capillary prostates, and then a long and convoluted ductus ejacula- 

 torius. What is remarkable in some butterflies {Pontia, e. g.\ is not 

 only the great length of the prostatic gland, but also the extreme 

 length and winding convolutions of the common terminal duct. 

 The structure of the introraittent organ in the Lepidoptera is such 

 as to preclude the repetition of the act, and they consequently live in 

 a state of compulsory monogamy. The bifid hooks on the terminal 

 segment of the dorsal valve of the penis, whilst they serve to retain 

 the female, prevent the entire extraction of the virile organ. 



With respect td the order Hymenoptera, Hunter has left some 

 good dissections of the male organs in the bee.§ The testes 

 are of a simple oblong form ; but, when we dissect away the cap- 

 sule or " tunica albuginea," we expose many long ca^cal tubes, 

 which, as they uncoil and float in the liquid, give a bushy cha- 

 racter to the gland. The sperm-duct rises from near the middle 

 of each testis, and soon swells into a large cellular reservoir common 

 to it, with the openings of two pyriform prostatic glands, whence a 

 common ductus ejaculatorius is continued to the base of the intro- 

 mittent organ. Newport has given a good description and figures of 

 the male organs in a wild bee {Athalia centifolia,Jig. 157.)} in which 



* CCLVIII p. 250. CCLVIII. p. 9. taf. 1—3. 



t CCXLI. tf. iv. xxxii. X CCLIX. Bd. 10. f. 10. 



§ X. vol. iv. pp. 34—41, Preps. Nos. 2332—2344. 



