74 NATUUAI, HISTORY 



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Ijy the folds of the rings, which seems a provision against their being 

 filled with the greasy matter upon which this insect feeds. 



The legs of these caterpillars, like those of most other larvae, are 

 of two sorts, horny or true legs, and memhranous or false legs* The 

 former contain in them the legs of the butterfly, the latter disappear en- 

 tirely in the perfect insect. These latter are a kind of nipple which the 

 insect can at its pleasure elongate, contract, and dilate, in most instances 

 terminated by a hook, which, however, is frequently wanting in some ge- 

 nera. They are more indispensable to the caterpillar than the horny 

 legs which only serve for walking, but do not aid in clinging to the 

 stalks or beneath leaves of plants. Their number varies from four to 

 ten ; Reaumur says, that he has seen some caterpillars of Tineidae that 

 had but one pair of membranous legs, but 1 have never discovered any 

 such. Their relative length likewise varies. The horny legs seldom 

 difl'er much in this respect, though in the Harpya fagi the first pair is 

 of ordinary length, but the other two very slender and as long as in the 

 perfect insect. 



The caterpillars of Rhopalocerata always have sixteen legs, as have 

 also the Sphingidae of the older authors. In the Bombycidae and rela- 

 ted races there is no exception to this, except that sometimes the last 

 pair of membranous feet is wanting or takes an unusual form. The 

 membranous feet, where the full number is found, are arranged in pairs 

 under the sixth, seventh, eighth, ninlli, and twelfth rings, so that the 

 fourth, fifth, tenth and eleventh rings are destitute of them. 



According to the number of membranous feet that have disappeared 

 and according to their contractility, caterpillars have been divided into 

 Psetido-Gcometrae, (FaJse-measurers,) Seml-Geoinetrac, ( Half -me usu- 

 rers,) and Geometrae, (Measurers.) The Pseudo-Geometrae are such 

 as have ten membranous legs, as most caterpillars, but in which the first 

 two or three pair are too short for them to be able to tise them in walk- 

 ing; thus when they walk the middle of their body forms an arc, as in 

 the Plusia, Euclidia, etc. The Semi-Geometrae have six or eight mem- 

 branous legs; they walk so as to form an arc or ring very much like 

 the Geometrae. The Geometrae are those that have four membranous 

 legs, such as the Geometra, Metrocampa, Hybernia, etc. These have 

 received the name of Measurers or Surveyors, (Geometers,) because in 

 walking they raise the middle of their body in the form of an arc by 

 bringing forward their hind feet to their foremost horny feet; they then 

 disengage the forefeet, and holding fast by their hind ones, push their 

 body forward in such a way that they seem to measure the space over 

 * Kirby and Rprncn call these prologs, (prdpedcs.) 



