NO. 2 ENCYCLOPEDIA OF INSECT ANATOMY — SNODGRASS 4I 



euphonious than "endoaedeagus") in distinction to the outer genital 

 parts as ectophaUic structures. The primary genital lobes thus become 

 the phallic rudiments and their branches phallomeres. The distal 

 aperture of the aedeagus is the phallotreme. 



This suggested nomenclature applies to only the major parts of 

 the male genitalia which can be consistently named on a basis of 

 homology. In all the insect orders, however, there are numerous 

 secondary developments, and these structures must be given special 

 names by workers in each order. 



Aedeagus (variously written also aedaeagus, aedegus, aedoeagus, 

 oedagus, edoegus, from Greek pi. oidoia, the genitalia + agos, chief 

 or leader) : The median organ of the male genitalia characteristic 

 of pterygote insects from Hemiptera to Hymenoptera. The ejacu- 

 latory duct opens into it. The aedeagus is thus, as the name implies, 

 the principal member of the genital complex. It is formed by the 

 union of the two mesal branches (mesomeres) of the primary geni- 

 tal lobes at the sides of the gonopore. The gonopore, therefore, 

 opens into the base of the aedeagal lumen, Avhich latter is thus a 

 secondarily added part of the genital exit passage, not a continuation 

 of the ejaculatory duct, and its distal opening, the phallotreme, is not 

 the gonopore. 



The aedeagus is commonly known as the penis of the insect, but 

 usually the whole organ does not serve for sperm intromission. The 

 spermatazoa are discharged from the duct into the lumen of the 

 aedeagus and then introduced into the female by eversion of the 

 membranous inner wall of the aedeagus as a vesicle, or a long slender 

 tube with the gonopore at its tip. This eversible tube, or endophallus, 

 thus becomes the functional penis. In some insects the spermatozoa 

 are incapsulated in a spermatophore, which during coition is attached 

 to the opening of the spermathecal duct of the female. With others 

 they are freely discharged either into the genital chamber of the 

 female, from which they may make their way into the spermatheca, 

 or they are introduced directly into the sperm receptacle. The en- 

 dophallus may become a highly developed complex organ in itself, 

 as in the honey bee, in which the outer part of the aedeagus is re- 

 duced to a pair of small plates guarding the phallotreme. 



Though the aedeagus is fundamentally a tubular organ, it takes on 

 various forms in different orders and families. In some Hymenoptera 

 the lateral parts of the aedeagus become separated as a pair of free 

 prongs (sagtttae) from a median penis tube. Among the Diptera 

 long rodlike processes (paraphyses) grow out from the aedeagal base. 



