608 THE METAMORPHOSIS OF FLIES. 
destroyed with the organs in which they ramify. Of the influence 
of the nervous system on the entire organism, there is nothing to 
be said since the change of form of the central parts ts accompa- 
nied by a complete histological transformation, as the interpent 
tration of their cell masses with fat demonstrates. 
The dorsal vessel does not now perform its functions. The 
animal now consists of a thin cellulose skin, with its contents 
partly destroyed, in part completely destroyed, and in part already 
concerned in the new formation of the organs. The entire fat 
body, cellulose tissue, of the larva, is lost in a liquid mass of fat 
globules and nuçlei, and they are mingled with the decaying mus 
cles, tracheze, etc. At the end of the first period the contents of 
the pupal body may be well compared with the contents of the | 
fertilized egg. All visible traces of animal life have ceased; Mf — 
action of the centres of the expression of animal life is suspended, 
and out of this chaos of elemental parts the organs are built up : 
anew. One essential difference from the development of the 
bryo only remains, that at no time are all the inner organs want . 
ing. External activity and decay occur simultaneously. But ye 
internal or external movements are wanting; sense organs 
nerves are wanting, and there can be truly said to be no où a 
impressions received, though an activity may be ascribed yar a 
central parts of the nervous system. Yet a regular flow of that . 
does not occur, and the only relative physiological action bs pie : 
of breathing, which here goes on as passively as in the egg; ™ ie i 
one case through the stigmata and tracheæ, in the other by goes : 
pores of the egg-shell. An active breathing process, such as 3 : 
on in the perfect state, is entirely wanting. — ele 
While the decay of the inner organs is going 0D; emselves 4 
_ taken place, the formative elements begin to develop th 
out of the cell-mass ; fat nuclei, fat globules, and flakes 
unite into round masses of nucleated spheres, 
of building up a membrane around themselves, a! : 
nucleus within, Already in the third, still more in the: ‘eal 
the fourth, day do the appendages of the thorax grow 10 jarval 
and all arise from a thin cellulose skin, an 
: + ag the fat 
cavity which fills up with fat globules and nuclei 48 
gradually breaks up. With this begins the m x 
the appendages and of the external form of the : 
definitive form; the period of formation of the body ° 
