l8 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 95 



THE EXTERNAL GENITALIA 



In a wide sense the external genitalia comprise all the secondary 

 sexual characters or modified organs that are concerned with sex 

 mating and egg laying, regardless of their position relative to the 

 opening of the genital ducts. They include copulatory organs, the 

 organ or organs of sperm discharge and intromission in the male, 

 and in the female the seminal receptacle, often a copulatory pouch, 

 and an ovipositor. Because of the variation in the position of the 

 genital apertures, most of the external genital organs have no 

 homology between the several major groups of arthropods, and very 

 different structures may be similarly modified to subserve the same 

 purposes. 



The copulatory organs may be defined as structures that serve to 

 hold the two mating individuals together during the insemination of 

 the female or of the eggs. In some cases copulation is effected entirely 

 by the intromittent organ of the male and the receiving pouch of the 

 female ; but more commonly the actual copulating, or holding of the 

 female by the male, is performed by the legs or other appendages, 

 which may be particularly modified for the purpose, and there may 

 be developed also special processes of the body specifically adapted 

 for clasping. In nearly all the arthropod groups some of the segmen- 

 tal appendages of the male are more or less altered in structure to 

 serve as clasping organs. In the insects the legs may be used for hold- 

 ing the female and are sometimes modified to this end, but the most 

 important copulatory structures of insects are the appendages of the 

 male genital segment, which are often highly modified and intricately 

 adapted to their function, though there may be present other appen- 

 dicular, or non-appendicular, structures that have a similar or acces- 

 sory function. If the female has any special organ of copulation it is 

 usually the pouch that receives the male organ, which in most cases 

 is a genital chamber (bursa genitalis) into which the oviduct opens; 

 but the copulatory organ may be the seminal receptacle (spermatheca) 

 itself, the orifice of which is sometimes specially adapted for the 

 reception of the apical part of the male intromittent organ. 



The intromittent organs of male arthropods include a great variety 

 of structures. Only in rare cases do the paired penes serve for the 

 actual introduction of the sperm into the female receptacles ; a direct 

 insertion of the two penes into the corresponding genital apertures 

 of the female, however, is said to take place in certain entomostracan 

 Crustacea, and it is possibly the mode of coition in the Ephemeroptera 

 among the insects. In general, however, where paired penes occur, as 



