452 



COMPARATIVE ANATOMY 



CHAP. 



tube. The anterior maxillee are short and ear-shaped with 4-jointed palps. The 2 

 many -jointed palps of the small lower lip lie on the sucking tube laterally. 



The various piercing and sucking mouth parts found among Insects have no 

 doubt developed independently of one another fi'om masticatory mouth parts. 



The special morphology of the mouth parts is therefore necessary for a knowledge 

 of the relationships of the members of one and the same order, but not for a know- 

 ledge of the phylogeny of the Insect-orders themselves. 



It sometimes occurs that the larvfe of certain Insects (Megaloptera among the 

 Ncuroptcra) have sucking mouth parts while the adults possess biting mouth parts. 

 This is an interesting fact, which shows how within a small group the larvfe may 

 develop sucking mouth parts in adaptation to special conditions of existence. In 

 those Lepidoptera, Diptera, Apihaniptera, and certain JJymenoptera which are provided 

 with sucking mouth parts, those of the larvte, when not degenerated, are of the biting 

 type. 



2. The Limbs of the Trunk. 



In the ancestors of the Antennata {Myriapoda and Hezapocla) in 

 •every case each trunk segment was certainly provided with a pair of 

 limbs, as is still the case in Peripatus and in the Myriapoda. 



In the Hexapoda only the 3 pairs of limbs of the 3 anterior trunk 

 segments have been retained, these 3 segments together forming 

 the thorax. Rudiments of extremities, however, are not. wanting, as 

 we shall jDresently see, on the segments of the hind-body even in the 

 Hexapoila. 



The trunk limbs are throughout distinctly jointed and consist of 



several parts, whose number 

 and constitution is extremely 

 important in classification. 

 The legs may be variously 

 formed according to their 

 special functions. We thus 

 distinguish ambulatory, 

 springing, smmming, seizing 

 legs, etc. Among the Myria- 

 poda the 1st pair of trunk 

 feet in the Chilopoda moves to 

 the head as a pair of maxilli- 

 pedes (Fig. 323, p. 464). 

 These are very strong, and 

 shaped like pincers. Their 

 basal segments are fused to- 

 gether into a plate in the 

 middle line. A poison gland 

 lying in the maxillipede itself 



Pig. 312.— Anterior end of the body of a female 

 Polydesmus complanatus, from tlie ventral side (after 

 Latzel). ('., Antennte ; st, stems of the mandibles ; v, 

 vulvi^i (apertures of the female sexual organs) ; yt, 

 ventral chord ; d, intestine. 



emerges at its terminal claw. 



In the Diplopoda (Fig. 312) the double segments {i.e. the rings 

 following the 4th or 5th trunk rings) have each 2 pairs of legs, while 



