418 Mr. T. H. Briggs on 
the common origin of those Zygenc at no remote date, 
and that a union of this nature was the result of a habit 
acquired as a form, not yet being lost in the species ; 
hence the species being, so to speak, new species, it would 
be inferential to suppose forms, not yet species, existing, 
yet to become species. If we examine the result of such 
a union, would it not bear strongly upon the title of any 
“form” to the rank of “species”? If the eggs resulting 
were fertile, and produced moths like either parent, it 
would go far to prove the parents only “forms” of each 
other, not yet sufficiently separated to attain to the rank 
of species. Ifthe eggs were fertile and produced hybrids, 
it would show that each parent was a species of itself, 
since they produced offspring unlike themselves, though 
probably closely allied, and their common origin of no 
very remote date. But if the eggs were sterile, would it 
not show that the line of demarcation was already estab- 
lished between those allied species, though the difference 
might be so slight, as to baffle our efforts to define it? 
I can find no instance on record, however, of even hybrids 
being bred from these unions, although we constantly catch 
specimens that if they are not hybrids, what are they? 
In his Monograph of the genus published in 1829, M. 
Boisduval observes, “ Je dois dire ici qu’il m’est arrivé 
quelquefois de trouver des espéces différentes accouplées 
ensemble, ainsi j’ai trouvé plusieurs fois la Filipendulee 
accouplée avec la Peucedani, et la Trifolii avec  Hippocre- 
pidis ; j’ai fait pondre les femelles pour obtenir des hy- 
brides, mais jamais je wai été assez heureux pour voir éclore 
les wufs résultant de ces marriages adultérins, quoique les 
ceufs des Zygenes éclosent tres facilement; il est possible, 
cependant, que quelques uns éclosent dans la nature.” 
So far as our present knowledge goes, therefore, the genus 
seems to consist certainly of a number of closely allied 
species, many of which species probably have different 
forms, some of which forms may be on the journey towards 
future species—the great difficulty yet remains, how to 
distinguish a local or Phytophagic ‘ form’ from a ‘species,’ 
it being impossible to apply the above test of an acci- 
dental natural union between two supposed species, 
although when that does occur, one can test species or 
forms by the result. We must therefore, in most cases, 
separate ‘form’ from ‘species’ by other means. In the 
‘ Entomologists Annual’ for 1861, Stainton, referring to 
the allied genus Procris, says, ‘‘ attention has been called 
