THE ENTOMOLOGIST. 63 



proved by the presence of fluid, vvliicb, on the creature's 

 emergence from the pupa slate, is observed to occupy a space 

 between them, sometimes even imparting to tlie 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 

 larvae a very similar arrangement of parts is observable ; but 

 while in the imago state the number of these " wings" never 

 exceeds four, in aquatic larva? 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 



