168 



AN INTRODUCTION TO ENTOMOLOGY 



Fig. 185.— Egg 

 Drosophila melan- 

 ogaster; m, micro- 

 pyle. 



The number and position of the micropylar openings varies greatly 

 in the eggs of different insects. Frequently they present an elaborate 

 pattern at one pole of the egg (Fig. 184); and sometimes they open 

 through more or less elongated papillae (Fig. 185). 



While in most cases it is necessary that an egg be fertilized in order 

 that development may continue, there are many instances of par- 

 thenogenesis among insects. 



The number of eggs produced by insects. — 

 A very wide variation exists in the number of 

 eggs produced by insects. In the sheep-tick, for 

 example, a single large egg is produced at a time, 

 and but few are produced during the life of the 

 insect; on the other hand, in social insects, as 

 ants, bees, and termites, a single queen may 

 produce hundreds of thousands of eggs during 

 her lifetime. 



These, however, are extreme examples; the 

 peculiar mode of development of the larva of the 

 sheep-tick within the body of the female makes 

 possible the production of but few eggs; while 

 the division of labor in the colonies of social insects, by which the func- 

 tion of the queen is merely the production of eggs, makes it possible 

 for her to produce an immense number ; this is especially true where 

 the egg-laying period of the queen extends over several years. 



The following may be taken as less extreme examples. In the 

 solitary nest-building insects, as the fossores, the solitary wasps, and 

 the solitary bees, the great labor involved in making and provisioning 

 the nest results in the reduction of the number of eggs produced to a 

 comparatively small number; while many insects that make no pro- 

 vision for their young, as moths, for example, may lay several 

 hundred eggs. 



With certain chalcis-flies the number of young produced is not 

 dependent upon the number of eggs laid ; for with these insects many 

 embryos are developed from a single egg. This type of development 

 is termed polyembryony. 



Modes of laying eggs. — Perhaps in no respect are the wonderful 

 instincts of insects exhibited in a more remarkable way than in the 

 manner of laying their eggs. If insects were reasoning beings, and if 

 each female knew the needs of her young to be, she could not more 

 accurately make provision for them than is now done by the great 

 majority of insects. 



