of a Species of Musca. 131 
as it is the exclusive attribute of the perfect insect, I have reserved the 
consideration of it for my general work on the Diptera, 
The adipose splanchnic tissue exists in three forms in the Sarcophaga, 
and performs an important part in the formation of the organs. That of 
the larva is in large sheets, or membranous folds drilled with holes ; but 
when the period of change approaches, it is converted into a net-work, 
the irregular meshes of which are granulated. In the nymph they appear 
as detached globules, floating in a copious liquid. These granules are 
plastic materials fully formed, and ready to enter into the construction of 
the parts. I have often succeeded in observing these organogenie mare 
rows disposed in linear series, dissolved in flakes, or laid out in plates, 
in order to form conduits, articulations, and membranes, in virtue of a 
law of organic affinity, not yet formally expressed, and of elective sensi- 
bility, with which human pathology furnishes us numerous examples. 
I have given provisionally the name of dorsal organ to an organ found 
in all the states of the Sarcophaga, in the median line of the back, and 
which is the analogue of the dorsal vessel of authors. In the Dipteron 
now under consideration, it is much more complicated than in other 
insects, and would seem consequently to have a physiological pre-emi- 
nence. We distinguish in it an avis and wings. The axis is a cord with- 
out cavity or divisions, fixed at one extremity to the hinder part of the 
dorsal tegument, and at the other to the origin of the chylific ventricle, 
without penetrating into the cavity of the latter. Its thoracic portion is 
naked, free, and a little attenuated. The wings are exclusively confined 
to the abdominal portion, They consist, for the third part of the length 
from the hinder extremity, of a double series of twelve reddish sphericles, 
which are sessile, and terminate in the same number of ligaments, and, 
for two-thirds of the anterior part, of a sort of epiploon or mesenteriform 
strawberry, composed of very small granulations, and supported on both 
sides by four ligaments. A minutely careful examination of the form and 
structure of this dorsal organ (new to science), proves that it has no ana- 
logy either to a heart or a vessel, and that consequently it cannot be con- 
sidered as a circulating apparatus. It is possible that it may be a secret- 
ing organ, but of a particular kind, and having no relation to the ordinary 
glands of insects. In regard to this part of the subject, I have establish- 
ed a classification of secreting organs which are pretty frequently met 
with among these animals, and its peculiar structure will exclude it from 
these. I have hazarded the conjecture, without attaching much import- 
ance to it, that the dorsal organ of the Sarcophaga may not be wholly 
unconnected with the formation and support of the tegumentary envelope 
of the Dipteron. 
The examination of the circulation of insects in general terminates my 
work. Although apparently foreign to my researches on the Sareophaga, 
it nevertheless arises out of them, from the details I have entered upon 
respecting the dorsal organ of this fly. For the solution of this problem, 
