NOTES AND MEMORANDA. 
145 
M. Bellesme made his principal study on Libellida depressa, and 
watched its disengagement from the pupal envelope. He saw the body 
swell out, then the head enlarge, the eyes grow round, and the wings 
spread out in an uniform manner. At the moment of extreme dis- 
tension, the volume of the body exceeded the dimensions it retained. 
While these phenomena were observed, little air penetrated the 
respiratory organs, but a slight prick of the abdomen produced instant 
collapse. In dissecting the swollen insects under water he always 
found the digestive tube filled with air and prodigiously extended. 
When the dragonfly disengaged his head from the pupal envelope, it 
took in air by its mouth as Keaumur supposed, and soon accumulated 
a considerable supply in the oesophagus, stomach, and intestine. In 
its dilatation the digestive tube drove the blood vigorously towards the 
sides of the body, towards the head, and the appendages, and by these 
means expanded the wings in a few minutes. Soon after the intestinal 
canal emptied itself, the body became flatter, acquired its true form 
and coloration, and respiratory movements were established. To 
leave no doubt as to the part performed by the air that entered the 
mouth, a simple experiment suffices. At the right moment let the 
entry of the air to the digestive tube be arrested, or let it escape by a 
prick. In each case the wings do not unfold, or they stop expanding.* 
Improvements in the Bivet-Leiser Microtome . — As this microtome 
has an increasing reputation and is becoming more widely known, it will 
not fail to prove interesting if some material improvements which have 
been made in it are published ; they have all stood a thorough test, in 
every way, in trials made at the Zoological Institute. Everyone 
has experienced that when the object gets in a certain position the 
knife has to be drawn too far back, in which case it may easily 
happen that the knife-carrier slips out of its place and falls with the 
knife on to the table or into the lap of the operator. In the first 
case the knife only is damaged, but the second case is positively 
dangerous, as the carrier is of considerable weight, and it is a common 
though a bad habit to clutch instinctively with the hands anything 
falling off the table. This defect is remedied as follows : — In the 
perpendicular side of the rut for the knife a horizontal groove is 
made, stopping short of the farther end, and about 1 * 5 mm. deep. 
On the knife-carrier is a knob, which moves without friction in the 
groove during the process of cutting. It is evident that when the 
knife is drawn too far back the knob comes to the end of the groove, 
and'the knife is prevented from falling out. 
The object to be cut, as is well known, can only be raised 1 centi- 
metre by the inclination of the sloping plane. When the object is 
larger it becomes necessary to loosen the screw and fix it higher. A 
number of suitable metallic plates have now been made which, when 
the cutting is commenced, are laid under the knife and screwed fast 
to it. When the object has been brought to the top, one or more of 
the plates are removed from beneath the knife, so that the latter sinks 
lower, according to the thickness of the plates; and the object requires, 
consequently, only to be drawn back again to enable the cutting to be 
continued. 
VOL. I. 
* ‘ Comptes Eendus,’ Jan. 7, 1878. 
M 
