and Warble Maggot. 
493 
provided (Fig. 6) with a compact, hard-tipped apparatus, very 
suitable, with due pressure from behind, to force open and 
gradually enlarge the fine passage (see Fig. 2) leading down in 
the early stage of attack, from the outside of the hide to the 
embryo swelling beneath. 
Fig. 6. — Spiracles and 
Tracheae of Young Maggot, 
The power of pressure possessed by the maggots at this period 
of their life is enormous, from their capacity of inflating them- 
selves with fluid until they are so hard that it is scarcely possible 
to compress them with the fingers, and likewise from their having 
(apparentlv) no power of discharging any of their contents. Thus 
they form living and growing plugs, quite capable of pressing 
back the tissues from around them, or from before the small hard 
tip ; but not subject (so long as they continue inflated) to being 
themselves compressed. I had opportunities of watching this 
process of inflation both in the worm-shaped maggots and when 
they were slightly more advanced in growth to a club or 
lengthened pear-shape. On placing them in fluid suitable for 
absorption (as in glycerine and water, in which they would 
live for as long as eighty hours, or until the spiracles sank 
completely beneath the surface) they became hard and shiny, 
and with little trace of the segments which are so clearly marked 
when the maggots are fully developed ; in fact, they were 
almost of a glassy smoothness, save for the short bands of 
minute prickles placed along a portion of the back. 
The size and shape of the perforation through the hide 
altered progressively with the growth of the maggot. At first 
this passage was very little larger at the lower than at the 
upper opening ; and though the walls of the perforation had 
now become smooth and shiny, I could not distinguish the 
