INTRODUCTION. 



13 



section may be conveniently classed under the term alternations of 

 generations, but the cases of alternation of two sexual generations, and 

 of sexual and parthenogenetic generations, are classified by Leuckart, 

 Glaus, etc. as cases of heterogeny, which they oppose to the other 

 form of alternation of generations. If special terms are to be adopted 

 for the two kinds of alternation of generations, it would be perhaps 

 convenient to classify the cases of alternations of sexual and gemmi- 

 parous generations under the term metagenesis, and to employ 

 the term heterogamy for the cases of alternation of sexual and par- 

 thenogenetic generations. 



The term Nurse (German Amme), employed for the asexual 

 generations in metagenesis, may advantageously be dropped alto- 

 gether. 



