. An introduction to zoology : for the use of high schools . pair of legsend in powerful claws perforated by the ductof a poison-gland, and are turned forwards tosupplement the three paiis of jaws. In theChilognatha, on the other hand, there is onlyone pair of maxillee below the mandibles, andthey are united to form a labium. The twoFig. groups further difier in that the Centipedeshave only one pair of legs to each segment, the Millipedes two iand that, while the Centipedes resemble the insects in theposition of the opening of the oviduct, this is near the head inthe Millij^ted
. An introduction to zoology : for the use of high schools . pair of legsend in powerful claws perforated by the ductof a poison-gland, and are turned forwards tosupplement the three paiis of jaws. In theChilognatha, on the other hand, there is onlyone pair of maxillee below the mandibles, andthey are united to form a labium. The twoFig. groups further difier in that the Centipedeshave only one pair of legs to each segment, the Millipedes two iand that, while the Centipedes resemble the insects in theposition of the opening of the oviduct, this is near the head inthe Millij^tedes. It will be apparent from what follows thatthese are much more important structural peculiarities than wefind separating the orders of Insecta from each other. Certain tropical worm-like forms {Perlpatus) which have the habits ofMillipedes, but whose segments bear unjointed appendages terminatingin hooks, are of interest as being intermediate between the Vermes andthe lower Arthropoda. A separate class (Protracheata) has been formedfor their 29. Returning to the locust audits allies, which are describedas the Orthoptera proper {0. geuuina), we must now proceedtoward thfe higher orders of insects, glancing, in the first place,at cex-tain forms associated by naturalists with the Orthoptera,on account of the structure of the mouth-parts and the absenceof a metamorphosis, but differing from them in that both pairsof wings are alike. The wings resemble those of the nerve- 212 HIGH SCHOOL ZOOLOGY. winged insects (Neuroptera), and, to distinguish them fromthese, the forms referred to are called here are the dragon-flies (LibeUulidoi), May-flies{Ejihemeridce), stone-flies {Perlidce), all of which have aquaticIarvs3 (into the tracheae of which air is absoibed throughjieculiar expansions of the body-wall known as tracheal gills),but there are also forms with terrestrial larvae, such,as theFsocidce (very small insects which live like plant-lice c
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Keywords: ., bookcentury1800, bookdecade1880, booksubjectzoology, bookyear1889
