102 jrLAIlsr FACTS FOR OLD AND YOUNG 



exist in liuman ova, is an undecided question ; but it is 

 probable that they do. 



Curious Modes of Reproduction.— A peculiar kind 

 of reproduction is observed in a variety of polyp, a 

 curious animal which very much resembles a flower in 

 appearance. It attaches itself to some solid object, and 

 then, as it grows, sends out little protuberances resem- 

 bling buds. Some of these separate and fall off, swim- 

 ming about as separate animals. These never become 

 like the parent polyp; but they lay eggs, which hatch, 

 and become stationary polypi, like their grandparent, 

 and in their turn throw oif buds to form swimming 

 polypi. In this case we have two kinds of generation 

 combined, alternating with each other. 



ParthenogenesiSo— Plant-lice afford a curious illus- 

 tration of a similar generation, known as partheno- 

 genesis. Males and females unite, and produce eggs. 

 The creatures produced by the hatching of eggs are 

 neither males nor perfect females. They are imperfect 

 females. They are all alike, so that no sexual union 

 occurSo Instead of laying eggs, they produce live young 

 like themselves, which appear to be developed from in- 

 ternal buds similar to the external buds of the polyp. 

 After this method of reproduction has continued for 

 nine generations, a few perfect individuals appear, and 

 the first process is repeated, "^yllile this budding proc- 

 ess has been going on, the original insect has con- 

 tinued laying ; and so great is the rapidity of this form 

 of reproduction that it has been estimated that even 

 at the end of the fifth generation, a single insect may 

 be the great great grandmother of nearly six billion 

 young ones. 



The common honey-bee affords another illustration 

 like the last. A virgin queen sometimes lays eggs, 



