AND PARTHENOGENESIS. 157 



the viviparous increase of the aphides, is altogether 

 overwhelming : 



Generation. Produce. 



1st, .... 1 Aphis. 



2d, . . . . 100, a hundred. 



3d, .... 10,000, ten thousand. 



4th, .... 1,000,000, one million. 



5th, .... 100,000,000, one hundred millions. 



6th, .... 10,000,000,000, ten billions. 



7th, .... 1,000,000,000,000, one trillion. 



8th, .... 100,000,000,000,000, one hundred trillions. 



9th, .... 10,000,000,000,000,000, ten quadrillions. 



10th, .... 1,000,000,000,000,000,000, one quintillion. 

 If the oviparous be added to the viviparous generation, the 

 result is thirty times greater ! l 



Forty years ago, it began to be observed that 

 similar phases of reproduction were to be witnessed 

 in the case of other animals. In 1819, Chamisso 

 (the author of Peter Schlemil, the Shadowless Man) 

 observed that the Salpa t one of the humblest of 

 Molluscs, perpetuated its race by alternations, and 

 he first gave to such a succession the name, Alterna- 

 tion of Generations. When he announced his disco- 

 very, Chamisso was " laughed at as a dreamer ;" but 

 the accuracy of his statements is now no longer 

 doubted. The Salpa is sometimes a simple, some- 

 times a compound animal sometimes existing soli- 

 tary, like a hermit in a wilderness ; at other times in 

 long chains of many individuals, like the associated 

 brotherhood of a thronged city. Each individual, 

 however, is distinct from its brother, and is capable 



1 Owen's Compar. Anal., p 414. 



