142 THE ENTOMOLOGIST’S RECORD. 
sents vermiform stages that the Orthopteron passed within the egg. 
The other is that it is descended from, and represents, the active pre- 
imaginal states of the Orthopteron. ‘That there is no retrogression in 
the sense that the other theory assumed, but merely modifications of 
various parts to meet various needs, modifications amounting in some 
cases to temporary suppression of parts and their reduction to 
imaginal dises, 7.e., collections of embryonic cells, undergoing no 
development until a very late stage in the life- history—this being, 
nevertheless, no retrogression, but really an advance. That this latter 
theory is correct seems proved for us by the crucial examples afforded 
us in the parasitic beetles, Meloé, Mylabris, Metoecus, and others, as 
well as other forms such as Stylops, which is perhaps truly a beetle. 
These hatch with good articulated legs, which they afterwards entirely 
lose and regain as imagines. In these, therefore, the vermiform stage 
is posterior to the articulate ones, and cannot, therefore, be descended 
from a stage anterior to that possessing limbs. 
When larval limbs are entirely absent the imaginal limbs exist in 
the larva as imaginal discs. How do they exist in the typical lepi- 
dopterous larva with 3-jointed corneous legs ? 
It is necessary to clear the ground a little, and ask ourselves what 
we definitely mean by this question, and what alternative answers may 
be or have been given. On the one hand we observe that in an 
Orthopteron at each moult the new leg is formed within the old one, 
and is withdrawn from it at the moult, or, more accurately, the new 
leg is the old one enlarged and grown, and freed from the external 
chitinous sheath, which had grown too small for it. Is the lepi- 
dopterous leg in this case? Is the imaginal leg really the larval leg 
grown and developed ? 
On the other hand, in the apod larva the imaginal leg is an 
imaginal disc. Is this also the case in the lepidopterous larva, the 
larval lee being got rid of as a larval appendage that has completed its 
life cycle and its usefulness, the new or imaginal lee entirely develop- 
ing from an imaginal dise within the body of the caterpillar ? 
I believe the former is the true answer, the larval leg is the 
imaginal leg also; but this answer must be modified to this extent, 
that the imaginal leg is so far different from the larval one, that it is 
to a great extent a new development, arising, therefore, to that extent, 
from imaginal discs, 7.e., reserved embryonal cells, but with this im- 
portant difference from the second answer I have suggested, that they 
are situated each within its own segment of the larval leg, or even 
more definitely, each in association with its own portion of each 
segment. The imaginal tarsus arises from the actual larval structures 
of the third joint of the larval leg and from embryonal cells situated 
amongst them, the imaginal tibia in the same way from the larval 
tibia, and so on, the trochanter and coxa being almost entirely in an 
embryonal state at the base of the leg. ‘This answer, which I support, 
is that that has been long held by the few entomologists who have 
paid any attention to the matter, and was believed to be supported by 
certain experiments of Reaumur’s* and Newport+, as to the effect on 
the imaginal structures of removing the larval legs. 
* Reaumur, Mémoires des Insectes, i., p. 365 (1734). 
+ Newport, Phil. Trans., 1844. 
