immature sexuality in Insects. 201 
of these Crustacea to be born invested in their maggot- 
like integument, and to pass the first half of their exist- 
ence in this condition, and we should have a condition 
very like that observed in the metamorphosis of the 
Metabola. 
With regard to the primitive ancestral forms of the 
Insecta we know nothing; but I think there can be 
little doubt that they were nearly allied to the existing 
Orthoptera. Nevertheless, I think it quite probable, 
that the larva may have undergone even greater modifi- 
cations than the imaginal forms, owing to the greater 
variability of the conditions to which larvz are sub- 
jected. 
I believe the great modification of the Insecta from 
their original type may, probably, have originated from 
modifications of the larva and imago re-acting on each 
other. The larva of one Ametabol form, Aphis, is known 
to reproduce agamically; a condition which I am not 
aware has ever been observed in a direct larva, but which 
occurs in acquired larval forms. 
I have drawn up a table, which gives the views I have 
arrived at, concerning the relation of the various larval 
forms in the Annulosa and Annuloida. (Vide p. 202.) 
The five spaces, one under the other, are intended to 
represent consecutive conditions. The forms in the 
lower lines in each column are supposed to have been 
produced by successive modifications from those above 
them in the same column. Thus the original larval and 
perfect forms of insects and trematoids are supposed to 
be unknown, and the pupa form is supposed to have 
been acquired before the present larval form. 
In conclusion, I may say that I only look upon the 
hypothesis which has made the frame-work of my present 
paper, as highly probable. When it first occurred to me, 
I mentioned my ideas to Mr. Darwin ; his kind encourage- 
ment, and the wish he expressed that I should publish 
my views were the main causes of my elaborating it 
to a greater extent. I then found it led me deeply into 
a most difficult labyrinth, which I have done my best to 
trace. I donoteven think, myself, that I have established 
my main hypothesis, but I trust I have brought together 
the seed which may, ultimately, produce good fruit. 
