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ILI. On the Development of Chloéon (Ephemera) dimidiatum.— Part I. 
By JOHN LUBBOCK, Esq., F.R.S., F.L.S., F.G.S. 
(Plates XVII. & XVIII.) 
Read January 15th, 1863. 
Introductory Remarks. 
BURMEISTER expresses, 1 believe, the opinion general among entomologists when 
he says that, excepting a few very rare anomalies, * we may observe four distinct 
periods of existence in every insect, namely, those of the egg, the larva, the pupa, and 
the imago” *. In most cases (as, for instance, in Diptera, Lepidoptera, Hymenoptera, and 
Coleoptera), the larva is said to be a fleshy maggot or caterpillar, quite unlike the imago; 
and these insects are therefore called by Prof. Westwood * Heteromorpha." In the 
Orthoptera, Hemiptera, Euplexoptera, and many Neuroptera, on the contrary, the larvze 
much more closely resemble the imago; and these groups are therefore called by Prof. 
Westwood ** Homomorphous " insects. In them, the pupa is said to differ from the larva 
in possessing wing-rudiments on the back of the two posterior thoracic segments. 
These differences, however, relate only to what we see in insects after birth ; while, 
if we are to treat the question in a philosophieal manner, we must examine the develop- 
ment as a whole, from the commencement of the changes in the egg, up to the final 
completion of the animal, and not suffer ourselves to be misled by the circumstance that 
insects do not all leave the egg in the same stage of embryonal development. Quatre- 
fages has well said, “ La larve n'est qu'un embryon à vie indépendante " t, expressing 
with his usual brillianey the idea which we owe, I believe, to Prof. Owenj, who says, . 
“The insects which are said to be subject to the semicomplete and incomplete meta- 
morphosis pass through the same kind and amount of change as those characterized 
by the obtected or coarctate pupa. The differences resolve themselves essentially into 
the place where, and the time in which, they assume and quit the vermiform state.” 
And again, “ The Orthopterous and Hemipterous inseets, characterized in entomology by 
a semicomplete metamorphosis, are, at one stage of their development, apodal and 
acephalous larvae, like the maggot of the fly; but, instead of quitting the egg in this 
stage, they are quiekly transformed into another, in which the head and rudimental 
thoracic feet are developed to the degree which characterizes the hexapod larvz of the 
Carabi and Petalocera.” I know not upon what authority this broad statement rests. 
Mr. Murray, indeed, at one time supposed that in some eggs of Blatta he had seen the 
larva in this grub state, but this statement has since been abandoned by its candid. and 
* * Manual, translated by Shuckard, p. 30. See also Curtis in the Journ. Agricult. Soc. vol. ii. p. 192. 
T Métamorphoses de l'Homme et des Animaux, p. 133. ; 
t Lectures on the Comparative Anatomy, &c., of the Invertebrate Animals, 2nd edit., pp. 423, 424. 
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