128 M. Dufour’s Anatomical and Physiological Studies 
rest to general physiology, and which divides the scientific naturalists of 
the present day, namely, the pretended circulation of insects. 
I hope the Academy will permit me to lay before it a sketch of this 
work on metamorphoses and circulation, which are the two natural divi- 
sions of the subject. 
After describing and figuring the larva, the nymph, and the winged in- 
sect, displaying the prodigious differences of those three states in the same 
individual, whose collective life presents a real trinity—after tracing the 
changes and developments, step by step, I have removed the tegumen- 
tary coverings, and, armed withm scalpel and microscope, have examined 
the various organic structures in their respective metamorphoses. I have 
endeavoured to initiate myself into the mysteries of organogeny. It is 
by dissectious of the living animal, a hundred times repeated, that I have 
witnessed these three organismsunrolled ; dissimilar indeed they are to each 
other, yet destined to become blended together and form only one. Ihave 
studied, in their inconceivable changes, the creation of the viscera of the 
larva, a headless, apodous, crawling, mandibular, carnivorous worm, 
growing with great rapidity, but of no sex, and without the power of 
generation ; those of the nymph, which, by its inertness and absolute in- 
sensibility, is the real image of a mummy, but concealing a living prin- 
ciple ; lastly, those of the perfect insect, which flies, runs, and is full of 
activity, sucks with moderation a subtile aliment, does not grow, has two 
separate sexes, and reproduces its kind by generation. I have attempted 
to catch, in the play of their material elements, the changes of these par- 
tial lives for a common or definitive life, which is the type of perfect or- 
ganism. I have been fortunate enough at times to seize those interesting 
moments when one organism became blended with the remains of another 
which was in the act of being destroyed—those fleeting instants, in which 
organs about to be lost still lent their aid to others just forming. 
In the interest of this threefold study of transformations, I have been 
led, by the modifications of the facts, to establish in the organism inter- 
mediate between the larva and the fly, and forming a series of links 
between the one and the other, namely, in that of nymph, three ages, 
phases or stages, which have not been remarked by my predecessors, and 
which are of great importance to the understanding of the progress of 
metamorphoses. The first age, w ich I call the jst transition, is that 
which immediately succeeds the passage of the larva intoanymph. There 
is still some organic connection of the latter with the envelope cast off by 
the larva. The second, the name of which is a sufficient definition, is the 
Sully-formed nymph. The latter is uniformly whitish. The third, which 
corresponds to the change of the nymph into a fly, is the second transition. 
The eyes have a violet tint. 
In the three changes of the Sarcophaga, the sensitive apparatus consists 
of two single central nerves, the brain and the thoracic ganglion, from 
which emanate all the nerves which distribute the movements of life 
throughout the various tissues. The brain is deeply bilobed, or is com- 
