M. H. Rathke on the Respiratory Process in Insects. 105 
C. Pupe and Nymphe. 
§ 29. In undisturbed pupze of Lepidoptera no movements of 
the body are to be detected, and therefore no movements that 
can be referred to the act of respiration. The same thing ap- 
plies to the pupz of Beetles, Hymenoptera, and probably of 
other orders of insects. Nor can it be perceived, on opening 
such pupz and irritating their trachez in various ways, that these 
vessels contract or dilate. 
From the absence of all such phenomena we might conclude 
that in the pupz of the above-mentioned insects the tracheary 
respiration is entirely interrupted. But, according to Sorg’s 
observations, pupz of Lepidoptera and Ants die, although not 
for some time, when kept in small receivers from which the ex- 
ternal air is completely excluded ; and these creatures consume a 
small quantity of oxygen, and give out a little carbonic acid. 
According to the observations of Reaumur and Martinet also, 
pupz die when their stigmata are covered with oil. If these ob- 
servations be correct (and there seems no reason to doubt them), 
the phenomena in question may be ascribed to two causes. In 
the first place, it is possible and conceivable that the air may 
penetrate the envelopes of the pupz as readily as those of birds’ 
eggs, and then enter ito a mutual action with the internal parts 
of the insects. The permeability of these envelopes by air and 
vapours is indicated by the fact that when dead larve or pup 
are exposed to the air, they dry and lose considerably in weight. 
In the second place, as the pup are not always exposed to the 
same temperature, the air contained in their trachez must under- 
go changes in its density ; and in consequence the trachee must 
sometimes give out a portion of their contents, and sometimes 
draw in a portion of the external air. 
In any case it is certain that the respiration of pupe can only 
be very weak. ‘This is shown by the observations of Sorg, and 
also by the circumstance that the pupz of many insects, e. g. the 
Bees, are enclosed in a nearly air-tight case, whilst others lie 
deep in the earth. This weak respiration in pupz is remarkable, 
inasmueh as it is in them that the most important changes in 
the form and number of the different parts of the body takes 
place. But it will not be difficult to give a satisfactory explana- 
tion of these phenomena. 
During the evolution of an insect within the pupa-skin, nearly 
all the fat and likewise a quantity of muscles and other structures 
disappear, but the materials of these parts pass into new combi- 
nations and serve for the evolution or even for the formation and 
evolution of other organs. They contain more or less oxygen 
in their composition; aud it is conceivable that this may suflice to 
