THE EEPEODUCTIVE SYSTEM. 131 



falls to the lot of the workers. Most other female insects lay their 

 eggs at some place where the young will be able to find food when they 

 hatch out, and the mother never in any way feeds or protects her 

 offspring; in most cases she dies before her brood emerges from the 

 eggs. But the wasps and bees are different in that nearly all of them 

 make a nest of some sort for the protection of the young larvae when 

 they hatch, in which also they store up food for them to eat. In many 

 species of wild bees all the work of constructing the nest, laying the 

 eggs, and collecting and storing food for the young devolves upon 

 the single female, as it naturally should, since insects do not ordinarily 

 have servants, and the males of most species are utterly irresponsible 

 in such matters. In some of the higher wasps, such as the hornets 

 and yellow jackets, however, the first females that hatcK out as adults 

 in the spring help their mother provide for a still larger family by 

 increasing the size of the house and collecting more provisions. 

 Nature designed them for this purpose, moreover, by making them 

 all sterile, allowing them to retain the maternal instincts, but de- 

 priving them of organs capable of producing offspring of their own. 

 Thus there is here a beginning of that division of labor which reaches 

 its highest development in the honey bee, where one form of the fe- 

 male is specialized entirely to produce the young and the other to 

 rear the brood, keep the home in order, gather the food, and ward 

 off enemies. The differences between the queens and the workers 

 are supposed to result from the different diet on which larvae designed 

 to be queens are brought up, but a more thorough investigation of the 

 food given to the different larvae of the brood is yet needed before 

 we can decide on the merits of this explanation. The work of numer- 

 ous investigators seems to have demonstrated conclusively that the 

 drone of the honey bee is always produced from an egg cell alone — 

 that is, from an unfertilized egg — while the queens and workers are 

 produced from fertilized eggs. The production of eggs that develop 

 normally without the addition of the male element is called partheno- 

 genesis. In a number of insects, such as some species of scales, a few 

 beetles, and some of the gall-forming Hymenoptera, there are no males 

 known, although the females are extremely abundant. Such cases 

 are often regarded by entomologists as examples of parthenogenesis, 

 and, if they are such, the result of the development of unfertilized 

 eggs is here the formation of females only. A few other insects, such 

 as some of the plant lice, produce eggs that develop without fertiliza- 

 tion into females or into both males and females, but such cases nearly 

 always occur in a cycle of alternating generations in which, at some 

 stage, all the eggs are fertilized. As far as is known the production 

 of males alone from parthenogenetic eggs is confined to the order 

 Hymenoptera. 



