form which will remain unchanged until the nymphosis. By virtue of
a remarkable variation, revealing a new vein of observation to the
entomologist, the Anthrax flies, in the larval state, assume two
successive shapes, differing greatly one from the other, both in
structure and in the part which they are called upon to play. I
will describe this double stage of the organism by the phrase
'larval dimorphism.' The initial form, that issuing from the egg, I
will call 'the primary larva;' the second form shall be 'the
secondary larva.' Among the Anthrax flies, the function of the
primary larva is to reach the provisions, on which the mother is
unable to lay her egg. It is capable of moving and endowed with
ambulatory bristles, which allow the slim creature to glide through
the smallest interstices in the wall of a Bee's nest, to slip
through the woof of the cocoon and to make its way to the larva
intended for its successor's food. When this object is attained,
its part is played. Then appears the secondary larva, deprived of
any means of progression. Relegated to the inside of the invaded
cell, as incapable of leaving it by its own efforts as it was of
entering, this one has no mission in life but that of eating. It
is a stomach that loads itself, digests and goes on adding to its
reserves. Next comes the pupa, armed for the exit even as the
primary larva was equipped for entering. When the deliverance is
accomplished, the perfect insect appears, busy with its laying.
The Anthrax cycle is thus divided into four periods, each of which
corresponds with special forms and functions. The primary larva
enters the casket containing provisions; the secondary larva
consumes these provisions; the pupa brings the insect to light by
boring through the enclosing wall; the perfect insect strews its
eggs; and the cycle starts afresh.