506 THE ANIMAL KINGDOM. 



of the Plecoptera, Trichoptera, and of Corethra among Diptera). In this case 

 the rectum is respiratory (Odonata] ; see supra. Or leaf-like processes are 

 appended to the end of the abdomen (Agrionida, among Odonata) ; or 

 similar leaf-like, filamentous, or tufted processes are attached laterally to 

 more or fewer of the abdominal somites (Ephemeridae, Calopterygidae 

 among Odonata, Trichoptcra^ Sialidae among Neiiroptera] ; or to the thorax 

 (Plecoptera], and then they are often retained by the imago side by side 

 with the stigmata *. These tracheal gills rise close to the rudiments of the 

 stigmata, which appear to be always present. There is a longitudinal 

 tracheal trunk from which tracheae pass off to the gills on one side, the 

 viscera on the other. The condition of an apneustic insect has been 

 secondarily acquired. 



The sexes are separate. Hermaphroditism when it occurs is due 

 only to malformation. The male differs in size, shape, &c. from the 

 female. The genital rudiments develope into a series of ovarial tubes s. 

 ovarioles, or testes. The latter are very variable in number and shape, 

 and the same statement is true also of the ovarial tubes. The anterior 

 extremities of the ovarioles are prolonged into filaments, the filaments 

 belonging to one side unite, and the common filament thus formed is 

 attached to the dorsal aspect of the abdomen or thorax. There are two 

 oviducts and two vasa deferentia. The latter sometimes dilate to form 

 vesiculae seminales. In the Ephemeridae the two male or female ducts 

 open separately, the former on the ninth abdominal somite in connection 

 with one or two copulatory organs, the latter between the seventh and 

 eighth somites, on the ventral aspect. The male ducts are similarly 

 arranged in Dermaptera, but in the genus Forficula the terminal portion 

 of one duct alone persists. In other Insecta the external genital apertures 

 are single, and there is an azygos portion invaginated from the integument 

 constituting the vagina in the female, or ductus ejaculatorius in the 

 male, the terminal portion of which is generally an intromittent organ. 

 Accessory female organs in connection with the vagina are the bursa 

 copulatrix and seminal receptacle, and other glands by which the ova are 

 fixed to some foreign object or enveloped in a cocoon or case. The male 

 possesses glands which unite the spermatozoa into spermatophores as 

 well as others of unknown function. The female aperture lies either 

 between the seventh and eighth or in the eighth somite of the abdomen ; 

 the male aperture in the ninth or tenth. In Lepidoptera the oviduct opens 

 on the same papilla as the anus, but the entrance to the bursa copulatrix 

 is in its normal position on the eighth somite. The two structures are 

 connected internally (see p. 160). The male copulatory organ in Odonata 

 is placed upon the second abdominal somite, and therefore far in front 

 of the sexual aperture. For the ovipositor see p. 500. 



1 Two branchiate Lepidopterous larvae are known. 



