On the Seasonal Dimorphism of Butterflies. 81 



of which, therefore, never exclusively propagated 

 themselves sexually " (Trematoda, Hydromedusce). 

 Under the other, or retrogressive form of meta- 

 genesis, Haeckel includes a " return from amphi- 

 genesis to monogenesis," this being the case with 

 all those species which now manifest a regular 

 alternation from amphigenesis to parthenogenesis 

 (Aphides, Rotatoria> Daphnidce, Phyllopoda, &c). 

 Essentially I can but agree entirely with Haeckel. 

 Simply regarding the phenomena of alternation of 

 generation as at present known, it appears to me 

 to be readily admissible that these multiform modes 

 of propagation must have originated in at least 

 two different ways, which can be aptly formulated 

 in the manner suggested by Haeckel. 



1 will, however, venture to adopt a somewhat 

 different mode of conception, and regard the man- 

 ner of propagation (whether sexual or asexual) 

 not as the determining, but only as the secondary 

 cause. I will further hazard the separation of 

 the phenomena of alternating generations (in their 

 widest sense) into two main groups according to 

 their origin, designating the cases of one group as 

 true metagenesis and those of the other as hetero- 

 genesis. 2 Metagenesis takes its origin from a 



2 It is certainly preferable to make use of the expression 

 " metagenesis " in this special sense .instead of introducing a 

 new one. As a general designation, comprehending meta- 

 genesis and heterogenesis, there will then remain the expression 

 " alternation of generation," if one does not prefer to say 



G 



