100 INSECT PHYSIOLOGY 



The transfer of sperm to the female which takes place at mating is 

 often an extremely elaborate process. The aedeagus or penis of the 

 male after entering the vagina may actually penetrate up the duct of 

 the receptaculum so that the spermatozoa mixed with the secretion 

 of the accessory glands are ejaculated directly into the spermatheca. 

 But more often they are discharged into the vagina or into the bursa 

 copulatrix which arises from it. 



In most insects the sperm are not conveyed to the female in a free 

 fluid but are enclosed in a membranous sac or 'spermatophore' 

 formed by the secretion of the male accessory glands. In the primitive 

 Collembola and Thysanura these sperm packets are just deposited at 

 random on little stalks ; on coming into contact with the female vulva 

 these spermatophores rupture and the spermatozoa enter the vagina. 

 But in many insects, such as Lepidoptera, crickets, many beetles, the 

 spermatophore is a complex structure which is formed during copu- 

 lation and transferred with its contents to the female genital tract. 



In some insects, such as the Gryllidae, the spermatozoa are 

 forced out of the spermatophore by the swelling of the inner walls 

 of the sheath. In any case, whether the sperm are discharged into the 

 female directly or by way of a spermatophore, they are next trans- 

 ferred to the receptaculum seminis or spermatheca. The mechanism 

 of this transfer is uncertain. Sometimes it is ascribed to pumping or 

 aspiratory movements within the female system; sometimes to active 

 migration by the spermatozoa in response to chemical or other 

 stimuli. In Rhodnius the accessory glands of the male secrete an 

 active material (perhaps identical with the material that causes 

 acceleration of the heart beat, p. 31) which acts on nerves to the ovi- 

 ducts of the female and evokes the peristaltic movements that trans- 

 fer the sperm to the receptacula. A similar secretion occurs in the 

 male accessory glands of many insects. Some idea of the complica- 

 tions is afforded by the fact that the receptacular duct in Lepidoptera 

 has a main lumen up which the sperm pass on their way to the 

 receptaculum, and a very fine subsidiary lumen, or 'fertilization 

 canal', in the substance of the wall along which they descend for 

 fertilization of the eggs. 



Fertilization does not take place until long after copulation, 

 usually just before the egg is laid. A few spermatozoa leave the 



