108 Journal New York Entomological Society. [Voi iv. 
First, the morphological, or groups of individuals more or less alike in 
appearance, form, structure or color; second, the physiological, or 
those forms of life capable of producing fertile offspring among them¬ 
selves. A species based on the morphological part of our definition I 
hold to be purely tentative (as we must apply the physiological part of 
the definition before we can be absolutely sure we have a valid species, 
but unfortunately it is only seldom, or after the lapse of much time, 
that specific value is capable of such proof). Now, my idea is that in¬ 
stead of relying to too great an extent on morphological differences we 
could fix the value of those modifications by analogy or comparative 
value. That is, if I should say that certain species (and giving a list, 
say of 25) represent my idea of specific value, I think students would 
get a better idea of what I meant than if I should spill any amount of 
ink in definitions and controversies. On the other hand, I could give 
a list of so-called species that did not represent my idea of true specific 
value. I can give a better idea of my meaning on this subject when I 
come to compare the value of our species and when I refer to them as now 
listed. Our species were described by a number of authors, and therefore 
represent to a large extent many individual ideas. However, our last 
Catalogue (that of 1884, by Mr. W. H. Edwards) gives the list of 
species according to the best knowledge and belief of our foremost stu¬ 
dent of the diurnals. 
I shall speak of the great variation in insects and say something of 
its causes, especially in the Lepidoptera. Some of our writers seem to 
have ignored absolutely the lessons these variations teach, especially 
when describing species. We have been so busy describing species and 
doing systematic work in this country that we have not had time to 
look into those interesting biological problems that have received so 
much attention abroad. There are many things which influence varia¬ 
tion in the Lepidoptera which are more or less well known, but this 
knowledge has not been sufficiently applied in describing species, or 
perhaps in some cases has been ignored. The principal causes which 
bring about variation are different geological formations and soils; dif¬ 
ferent foods; season ; climatic conditions; horizontal and vertical dis- 
distribution or what might be called longitude and latitude; altitude 
which produces apparently the same effect as vertical distribution. 
1 hese causes may all be covered in a general way by calling them the 
effects produced by geographical distribution. Heat and cold may act 
locally at different times or is in other cases a factor in vertical distribu¬ 
tion. “ Succulent overgrown herbage produces large pale colored im- 
