24 NOTES ON 
The first and second exuvia which it sheds ex- 
hibits the structure of these spines very dis- 
tinctly, and, from its transparency, allows of 
considerable amplification. 
The larve of the Libellula depressa, and some 
other species, are devoid of these leaf-like 
appendages. They possess a curious hydraulic 
apparatus, which Reauwmur* informs us they 
employ for propelling themselves, and also for 
respiration. ‘This apparatus, which forms the 
cavity of the lower part of the abdomen, it can 
dilate or contract at pleasure. When closed by 
the muscular action of the larva, the water with 
which it was previously filled is expelled, and, 
by its action against the stationary fluid, the 
creature is urged forward; when again dilated, 
a fresh portion of water is admitted, and the 
pumping is repeated, at the will of the creature. 
The anatomy of these parts, by which the air 
is absorbed for the purpose of respiration, is 
briefly described by Kaurby and Spence, in 
vol. iv., p. 16, of their Introduction. 
The young larve of the Libellula grandis 
swim with great activity, inflecting the body 
laterally as they advance, and assuming the 
position exhibited in the annexed sketch, the 
* Reaumur Mem. Insects, vol. vi. 
