April, 1919 Bulletin of the Brooklyn Entomological Society. 35 
which is practically “non-metabolous,” and one which is practi- 
cally holometabolous) descended from an ancestral group con- 
taining some “non-metabolous”’ forms and also some holometab- 
olous forms; and we would naturally expect that the coleopter- 
ous representatives of the ancestral group, being holometabolous, 
would be somewhat nearer to the derived holometabolous group 
(7. e., the neuropteroid superorder, comprising the Neuroptera, 
Hymenoptera, etc.), while the plecopterous, embiid and der- 
mapterous representatives of the ancestral group, being “ non- 
metabolous,” would be somewhat nearer to the derived “non- 
metabolous” group (1. e., the psocoid superorder, comprising the 
Psocidz, Mallophaga, etc.), and this is true to some extent. 
The derivation of the higher forms, as given above, would 
readily account for the presence of a metamorphosis in one de- 
rived group of higher insects, and its practical absence in the 
other derived group of higher insects (despite the fact that both 
derived groups are very closely related), since both of these de- 
rived groups are descended from a common stock containing 
some forms which exhibit a pronounced metamorphosis and some 
forms which do not. This, however, does not account for the 
origin of metamorphosis in some members of the ancestral group 
itself, although the fact that there is a marked tendency for such 
lower insects as the Odonata to develop a slightly different type 
of immature form from the adult (a tendency which is also 
evidenced by the Plecoptera, which are among the lowest repre- 
sentatives of the ancestral group giving rise to the higher forms), 
may give some hint as to how metamorphosis arose. 
I am inclined to think that such a tendency for the immature 
forms to differ from the adults gradually arose among primitive 
insects, possibly through mutation, or through the proper combi- 
nations of hereditary factors enabling to re-assert itself, a ten- 
dency which had remained “latent” through generations of 
forms descended from Crustacea-like forebears (which showed 
a marked tendency toward a metamorphosis). Such a tendency 
for the immature forms to differ from the adults might eventu- 
ally result in the production of stages which could enter an en- 
vironment to which the adult, as such, was unable to adapt itself,, 
or stages which might be able to resist temporary conditions 
