ALTERNATION OF GENERATIONS. 303 



Eecovering from the stupor into which we are thrown 

 by facts like these, let us observe that here, as in the 

 case of the Asciclians and Polypes formerly mentioned, 

 an alternation of generations takes place; the parent 

 producing a child unlike itself, and that child in its 

 tm"n finally producing one like its grand-parent. " The 

 winged and perfect Aphis produces a wingless hexapod 

 larva ; this wingless larva produces at last a winged 

 and perfect insect." The reader may imagine how great 

 was the sensation produced in the scientific world by 

 these announcements, and how many theories were 

 pro23ounded in explanation ; we must not pause here to 

 consider them, but proceed with our history. 



The last date was 1745. In 1819 a Germanised 

 Frenchman, known to all lovers of romance as the 

 author of Peter Schlemil, made a discovery in Natural 

 History which was almost as incredible as his Shadow- 

 less Man. Whether this will endear the name of 

 Chamisso still more to his admirers may be a question. 

 Literary men will point with some satisfaction to the 

 fact that a novelist was the discoverer of a form of re- 

 production unsuspected by the profoundest zoologists. 

 They may also remember that the luminous doctrine of 

 plant-morphology was the discovery of the greatest of 

 our modern poets ; and that the great Haller himself 

 was a poet and litterateur before, in later life, he de- 

 voted himself with such splendid success to physiology. 



In Chamisso's day, naturalists knew two distinct spe- 

 cies of the curious mollusc named Scdpa, an indescrib- 

 able animal, transparent as crystal, and of irregular 



