Asti 
THE PHYSIOLOGY OF RESPIRATION IN INSECTS. 373 
In other preparations the pupa-sheath is seen to be con- 
nected with the base of the inter-segmental spiracular cornu. 
I am inclined to believe that the pupa-sheath of Weismann is 
the result of a second ecdysis; and, in parts, at least, the pupa- 
sheath is distinctly formed of several layers closely pressed 
together. It is probable, I think, that two or more ecdyses 
occur, which are either partial or complete ; but owing to the 
extreme thinness of the shed layers it is extremely difficult to 
trace them. It appears to me probable that the first ecdysis 
is only partial, and is limited by the extent of the discs at the 
time of its occurrence, as there is no appearance of a con- 
tinuous membrane enclosing the whole of the limbs in a single 
sheath, a condition which could hardly fail to exist if a com- 
plete ecdysis occurred before their evolution. The only indica- 
tions of more than one ecdysis in the pupa are the early 
separation of the prothoracic stigmatic cornua, and the lami- 
nated structure of the pupa-sheath. 
The Posterior Thoracic and Abdominal Spiracles of the imago 
are all new formations in the nymph, which had no pre- 
decessors in either the larva or pronymph; but they are 
developed in precisely the same manner as the larval spiracles 
and the anterior thoracic spiracles of the nymph; that is, by 
the invagination of the cellular integument, which forms the 
spiracle and vestibule, in relation with a newly-formed tracheal 
vessel, which is developed from one of the tracheal branches 
distributed to the integument. 
4. THE PHYSIOLOGY OF RESPIRATION IN INSECTS. 
It has been asserted that the respiration of insects, when 
in full activity, has the same energy as in the higher verte- 
brates ; this statement is, however, misleading, and cannot be 
accepted without modification. 
From the observations of Regnault and Reiset [157], it 
appears that insects absorb a weight of oxygen equal to 
rgloath of their body weight per hour. This estimate does not 
differ materially from that obtained amongst moderate sized 
