REPRODUCTION OF INSECTS. 269 



Some Peculiarities in Reproduction. 



Many Insects, such as aphides, silk-moth, and queen-bee, are exceed- 

 ingly prolific. The queen-termite goes on tor a time laying thousands of 

 eggs " at the rate of about sixty per minute " ! 



The store of spermatozoa received by the female, and kept within the 

 receptaculum seminis, often lasts for a long time, — for two or three 

 years in some queen-bees. Sir John Lubbock gives the remarkable 

 instance of an aged queen-ant, which laid fertile eggs thirteen years 

 after the last union with a male. 



Parthenogenesis, or the development of ova which are unfertilised, 

 occurs normally, for a variable number of generations, in two Lepidop- 

 tera and one beetle, in some coccus-insects and aphides, and in certain 

 saw-flies and gall-wasps. It occurs casually in the silk-moth and 

 several other Lepidoptera, seasonally in aphides, in larval life in some 

 midges (Miastor, Ckironomus), and partially or "voluntarily" when 

 the queen-bee lays eggs which become drones. The unfertilised eggs 

 of the hive-bee become drones, the fertilised become queens (perfectly 

 sexual females) or workers (abortively sexual females), according to the 

 richer or plainer diet given to the grubs. Parthenogenetic ova 

 (in water-fleas, Rotifers, etc.), are believed to form only one polar 

 body ; the egg which becomes a drone forms two as usual, but the case 

 of the bee is in several respects exceptional. 



A few insects hatch their young within the body, or are " viviparous." 

 This is the case with parthenogenetic summer aphides, a few flies, the 

 little bee-parasites Strepsiptera, and a few beetles.. 



Development of the Ovum. — The tubes which compose the 

 ovaries and lead into the oviducts start from thin filaments, 

 the ends of which are usually connected on each side. 

 Those thin filaments consist of indifferent germinal cells, all 

 of them potential ova. 



But in most cases only a minority of these cells become 

 ova, the others become nutritive cells, which are absorbed by 

 the ova, and follicle cells which line the walls of the ovarian 

 tubes and help to furnish the egg-shells. 



There may be, indeed, ovarian tubes without nutritive cells 

 (e.g., in Orthoptera), and then each tube is simply a bead- 

 like row of ova, which become larger and larger as they 

 recede from the thin terminal filaments and approach the 

 oviducts. In other cases, the bead-like row consists of ova 

 alternating with clumps of nutritive cells (e.g., in Hymenop- 

 tera and Lepidoptera). In other cases, the nutritive cells 

 mostly remain in the terminal region, but their products pass 

 down to the receding ova. 



