THE ENTOMOLOGIST. 68 
proved by the presence of fluid, which, on the creature’s 
emergence from the pupa state, is observed to occupy a space 
between them, sometimes even imparting to the part the 
appearance of an inflated bladder. Nevertheless, as the 
insect rapidly advances towards maturity, the blood retires 
into the trunk, and the bladder is seen to shrink and finally to 
collapse, while the two membranes approach, unite, and hence- 
forward become one and indivisible. A word remains to be 
said about the encased windpipes. These are generally divided 
and branched, the branches taking many directions, fre- 
quently anastomosing, and thus forming a complete network 
or frame, which supports the membrane, distended over them 
like the canvas over the ribs in the sails of a windmill, and 
the two united constitute the so-called “wing.” In aquatic 
larve a very similar arrangement of parts is observable; but 
while in the imago state the number of these “ wings” never 
exceeds four, in aquatic larve of hexapods it often rises to 
twelve or fourteen; then they are employed as swimming 
organs, in addition to their use as respiratory organs; but 
the name of “windpipe,” or of some equivalent in the 
language of science, is retained, while in the perfect insect 
the name of “ wings” is universally applied. 
2. Octopods, which at every period of their existence 
possess eight legs,—as mites and spiders, and all spider-like 
animals; in these there is never any indication of wing. 
[These are the Arachnides of Latreille, | 
3. Anisopods, whose legs are mostly ten, but often more, 
and which are for the most part marine animals,—as crabs, 
lobsters, crayfishes, prawns, and shrimps. [These are the 
' Crustacea of Latreille. ] 
_ 4, Myriapods, which possess a multitude of legs, and 
which are familiarly known as centipedes, or hundred legs. 
[These are the Myriapoda of Latreille. } 
The essential characteristic of Exosteate structure, neces- 
sitated, as I conceive, by the external situation of the 
principal organs of support, is the fusion, amalgamation, or 
inseparability, of several systems of organs. The organs of 
support, circulation, and respiration, instead of being detached, 
as in endosteates, are so inextricably involved as to defeat 
the attempts of the most skilful anatomist to separate them ; 
indeed, it seems a necessity that the organs of respiration 
