ae MEP RIE Bere oT A tp eee Ree Fe 
Brats eee eee hee een ee eae eee Te gee 
Sg eS eet ge eh eee 
THE METAMORPHOSIS OF FLIES. 665 
the Lepidoptera the origin of the thoraz is from the hypodermis of 
the larva; that no thoracic disks are developed within the body, 
but that the appendages of the thoracic segments grow by a direct 
metamorphosis from the limbs. The wings alone have a special 
mode of development and in a very peculiar way. 
I think that the kind and mode of formation of the thorax in 
the pupa of insects have the closest connection with, at first sight, 
a very subordinate circumstance, the presence or absence of true 
limbs in the larva. T think, that especially where the three segments 
of the larva immediately following the head bear appendages, the 
corresponding appendages—the legs—of the adult insect, are formed 
a simple metamorphosis; while on the other hand, when these 
limbs are wanting in the larva, there are found thoracic scales within 
the body of the larva ; and not only the appendages but also the walls 
of the body are new structures. e 
All my observations, new and old, agree with this view ; among 
others the earlier observations on the larva of the gnat, already 
Spoken of, which have only anal limbs, but no typical segmental 
appendages, and in which the structure of the thorax is the same 
as in the Muscidæ. 
When it is said that the life of the insect is latent in the pupa, 
that the usual functions of animal life, such as motion and sensi- 
bility are wanting, I might speak of the Muscidæ alone, and say 
this of all insects with a similar mode of formation of the thorax. 
There comes into consideration here, not only the greater or less 
independence of development, the more or less marked absence of 
the larval organs, but also the period of the formation of the pupa. 
In the Tipulid larva, noticed above, the larval and pupal states are 
more intimately blended than in the Muscids. The thorax and 
ead of the pupa are already fully formed, while the larva is ac- 
tively swimming about. When the larva skin is cast off i the 
muscles of the pupa are already at work; the functions of animal 
life suffer no interruption. 
But in the Muscidæ the loss of the larval parts precedes the 
formation of the body of the pupa. Hence we perceive no mo- 
tion, and in fact the animal life is latent. The circulation of the 
~ blood ceases, the peripheral nervous system is destroyed, and the 
Central system loses any power of action; at the same time all 
the inner organs become incapable of farther functional condi- 
- The development of new systems of organs begins with 
