344 



GENERAL BIOLOGY 



In all female insects there are a pair of ovaries (Fig. 222) usually 

 formed of many small tubes called ovarioles. From the ovaries the 

 oviducts pass out into a terminal region, the vagina, which is sometimes 

 also paired. This latter organ is usually formed by an invagination from 

 the outer part of the body until it meets the oviducts, while near this, 

 or branching off from it, there is a receptaculum for receiving and hold- 

 ing the male sperm received during copulation. 



Then there are accessory glands which secrete a sticky substance or 

 cement as the eggs pass through the oviduct. These glands are known 

 as colleterial or sebific ( ) glands which open in turn 



into the dorsal portion of a capacious pouch, the bursa copulatrix, 



through a duct. This bursa rests 

 on, and opens directly into, the ovi- 

 duct of the female. Grasshoppers 

 have an external hard posterior re- 

 gion of the body known as an ovi- 

 positor (Fig. 225). 



The males possess a pair of 

 testes usually formed of many small 

 tubes connecting with two ducts, the 

 vasa deferentia which carry the 

 sperm to the terminal portion called 

 an ejaculatory duct, which may have 

 one or two openings. This external 

 opening may be formed by the union 

 of both vasa deferentia or by an in- 

 vagination meeting these ducts. 

 The seminal vesicles, usually paired, open from either the vasa 

 deferentia or the ejaculatory duct. Here sperm are stored. Often there 

 are accessory glands whose secretion unites the sperm into packets 

 known as spermatophores. There may or may not be an external copu- 

 latory organ though in the grasshopper there are a pair of these, called 

 cerci. Often there are also external hard parts as in the female though, 

 of course, these are not ovipositors. 



The sperm are placed in the seminal receptaculum of the female by 

 the male and may remain there for many years. The queen bee only 

 copulates once, and that on her first and only flight, and yet the sperm 

 have remained alive so that eggs which were laid thirteen years after- 

 ward were fertile. 



There are a few insects which give birth to living young, such as 

 the "parthenogenetic summer aphids, a few flies, the little bee parasites 

 Strepsiptera, a few beetles and cockroaches," but by far the greater por- 

 tion lay eggs, the young then developing from these. 



When eggs develop which have not been fertilized, birth is said to 

 be by parthenogenesis ( ). This occurs normally, 



Fig. 225. 



Rocky Mountain locust : a, a, a, Female in 

 different positions, ovipositing ; b, egg-pod ex- 

 tracted from ground, with the end broken 

 open ; c, a few eggs lying loose on the ground ; 

 d, e, show the earth partially removed to il- 

 lustrate an egg-mass already in place and one 

 being placed ; /, shows where such a mass has 

 been covered up. (After Riley). 



