GREEN-FLIES AND PLANT-LICE 331 



water shrimp called Apus, which goes on multiplying in 

 this manner in wayside ponds for years, thousands of 

 female individuals being produced in successive seasons, 

 laying their eggs and carrying on the race for an indefinite 

 time until at last one fine day we do not know why 

 then and not before, that rare creature a male Apus is 

 hatched. Why these and one or two other such small 

 shrimps and insects are able to set aside the almost 

 universal law as to the necessity for fertilisation of 

 the egg-cell by a sperm-cell, naturalists have not yet 

 found out. It is quite certain that these exceptional 

 creatures have been derived from ancestors which had 

 their eggs fertilised in the regular way, and that this 

 elimination of the male is a special device, an innova- 

 tion. 



There are incomplete attempts at it in other insects. 

 Thus it has been discovered that the queen bee produces 

 only females from the eggs which are fertilised before she 

 lays them. When the stock of sperm-cells which she 

 received from a drone in her nuptial flight is exhausted, 

 or if we carefully remove by a painless operation the 

 internal sac in which they are stored, the eggs are no 

 longer fertilised, but they are not rendered sterile or 

 ^abortive. They develop into drones ! And drones or 

 male bees are produced in no other way, and only drones 

 are so produced, never worker-females (so-called neuters) 

 nor queens. 



Another curious fact is that in rearing moths in 

 captivity some naturalists have quite unexpectedly found 

 that when they have hatched out female moths from the 

 chrysalids and kept them from the moment of hatching 

 quite apart from the male moths (which are of another 

 size and colour, and easily distinguished), these females 

 will sometimes lay eggs unfertilised eggs which give 

 birth to caterpillars, which feed and complete all their 



