195 
to Bøving should be closed cannot provide the animal with 
sufficient oxygen. Only by means of active inspiration the larva 
can get oxygen enough, we must therefore maintain that there 
cannot be any closing membrane to prevent the free current of air. 
I have corresponding analyses of the air in the cocoons and 
in the intercellular spaces only from the summer, nevertheless we 
can learn a little concerning the respiratory conditions during 
the winter. 
The analyses have shown that the O,-percentage in the 
intercellular spaces decreases during the winter, but so far as I 
have seen never so low as to zero. 
The lowest value I have found is 0,4 ”/o O,, and at the 
time the water had been covered with ice almost a month. But 
under these conditions the animal's metabolism must be very low, 
and it is far from sure that the respiratory conditions are worse 
during winter!) than during the summer. 
Summary. 
The Donaciae larvae cannot breathe the oxygen dissolved in the 
water; the only way in which the animal can get oxygen is by 
active inspiration through the canals in its hooks, from the air 
in the intercellular spaces of the roots of aquatic plants on which 
they live. 
The cocoon is airtight; the air in it cån therefore only be 
renewed by diffusion of the air in the intercellular spaces with 
which it is in communication. 
1) Deibels assertation, that "Im Winter hårt natiirlich die Sauerstoff- 
zufuhr auf. Das Tier ist dann auf die im Kokon eingeschlossene 
Luft angeweisen” is consequently incorrect. 
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