69 MR. J. LUBBOCK ON THE DEVELOPMENT OF 
ingenuous author. With the exception of this genus, I am not aware that the develop- 
ment of any Orthopterous or Hemipterous insect has been worked out. 
Two memoirs bearing on the subject have, however, since appeared, namely, Zaddach's 
“Die Entwickelung des Phryganiden-eies," and Huxley's memoir on Aphis, which 
appeared in the Transactions of this Society. Zaddach figures (fig. 19) and describes 
a state in which the embryo of Phryganea is a grub, with an imperfect, though seg- 
mented, body, but without any appendages; yet, he says, this condition lasts only for 
a short time, and may therefore easily be overlooked. Prof. Huxley also* has shown 
that there is, in the development of Aphis, a particular period at which the embryo 
presents, on the sternal side, traces of segmental divisions, without having even rudiments 
of legs. Thus then it appears that in both these cases the so-called * larva" is preceded 
by an apodal body, corresponding in some respects with the grubs of Diptera. It is 
unnecessary to remark, that the change from this grub-like embryo to the so-called 
“larva ” is produced by gradual modification, and not by any process of moulting. But, 
in considering the matter, we must also bear in mind that the apodal body of the embryonic 
Aphis or Phryganea is in a very different condition from the maggot of a fly. Not 
only are the internal organs, so far as our information goes, entirely undifferentiated, 
but the dorsal walls themselves are not as yet formed. ! 
But however this may be, and even in the case of insects with an incomplete meta- 
morphosis, it is the general opinion of entomologists that the life may be divided into 
three periods, each marked by a change of skin and an alteration of form. “After the 
first change,” says Burmeister t, “the larva has merely increased in size; but during 
this second period of its existence, the rudiments of the wings form beneath the skin; 
consequently, after the second moulting, these incipient wings present themselves 
externally as small leaves, which cover the sides of the first abdominal segment: 
these larvee are called nymphs, being analogous to the pupa-state of other insects. 
When this pupa again moults, the insect attains its perfect condition," 
Prof. Owen also, although, as we have seen, he considers that the period corresponding 
to the larva of Diptera, Lepidoptera, &c., is, in insects with an incomplete metamorphosis, 
passed in the egg, still appears to consider that the life even of these last falls into 
three well-marked periods. 
` T shall, however, show that in several insects there is no such well-marked, threefold 
division; and that, in the Ephemeridæ at least, the young insect gradually attains its 
perfeot condition through a series of more than twenty moultings, each accompanied by 
an change of form. Fig. 10 represents the state at which the first rudiments, or 
rather indications, of wings make their appearance, in the form of a searcely perceptible 
production of the posterior meso- and metathoracic angles; and it will at once be per- 
ceived that the amount of change is very slight indeed. 
Probably our opinion has been too much influenced by the well-known metamorphoses 
of Lepidoptera, and we have expected to find the same changes and the same uniformity 
throughout the insect-world. 
Even = however, a certain number of exceptional cases are upon record, and we 
#« : 0 ا‎ 7 : 
z = sees n and Morphology of Aphis,” Linn. Trans. vol. xxi. part3. + Loe. cit. p.429 
