On the Seasonal Dimorphism of Butterflies. 99 



degraded sexual insects, or as true larvae which 

 had attained the power of asexual propagation. 

 Their propagation would be considered to be par- 

 thenogenesis ; and as it could not be denied that 

 heterogenesis was here manifest, the mode of de- 

 velopment of their particular kind of propagation 

 might be proved, i. e., it might be demonstrated, 

 that the generations now parthenogenetic were 

 formerly mere reproductive larval stages. 



I have only offered these last observations in 

 order to show on what uncertain ground we are 

 still standing with regard to this subject when- 

 ever we deal with the meaning of any particular 

 case, and how much still remains to be done. It 

 appears certain that the two forms of cyclical pro- 

 pagation, heterogenesis and metagenesis, origi- 

 nate in entirely distinct ways, so that it must be 

 admitted that, under these circumstances, the 

 idea of the existing conditions respecting the 

 true genesis may possibly be erroneous. To in- 

 dicate the manner in which the cyclical mode of 

 propagation has arisen in any single case, would 

 only be possible by a searching proof and com- 

 plete knowledge of existing facts in addition to 

 experiments. 



H 2 



