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Transactions of the Society. 
packed away inside a pocket placed on the ventral side of the anal 
segment, and this is the position they are found in if the larva is 
first narcotized before being killed and fixed for mounting (fig. 10). 
Some of the accounts referred to are records no doubt prepared 
from examination of mounted larvae which have first been dropped 
into the killing and fixing fluid and not previously narcotized. 
Under these conditions an effort would be made to escape from the 
effects of the surrounding medium, and, in a state of excitement or 
irritation, the hooks had been forced out. 
This is the position of the hooks on specimens I have prepared 
without narcotization. On two purchased slides and thirty other 
slides subsequently examined the hooks were internal, as described 
Fig. 9. — Double row and two large hooks on anal segment, with detail of 
single pair of hooks. 
above, and on enquiry we found that the method of preparation 
included narcotization before killing. 
It was necessary to try out some experiments on live specimens 
before it could be decided whether the organ referred to was fixed 
or movable. Six larvae were secured. The first was placed under 
the microscope in a live box which had a screw-on cover instead of 
the regular sleeve fitting. This enabled us to apply very gentle 
pressure, just sufficient to hold the creature across the thorax. 
The tail end was promptly swung round and held by the jaws, 
the larva probably being under the impression it had secured the 
attacking party. At each nip it received from its own jaws the 
