INSECTA 



529 



(5) "Note sur quelques pentastomes," Bull. Acad. roy. d. Sci. de Belg., 1857, 26, 

 2 s., ii (5), pp. 29-30, v. Beneden. 



(6) " Ueber das Pentastoma in de gekrosdrusen den Schafe," Repert. d. Thierh. Sttittg., 

 1861, xxii, pp. 37-38, Collin. 



(7) " Eine Linguatula aus der Mesenterialdriise des Schafes und Dromedars als zweites 

 ungesche. Stadium von Pent, taenioides," Notiz. u. Tagsber. u. d. Geb. d. Nat. u. Heilk. 

 Jena, 1862, v, pp. 127, 128, Colin. 



B. INSECTA (Hexapoda). 



Three separate regions can always be distinguished in the body of insects, 

 namely, the head, thorax and abdomen. The HEAD is a roundish unsegmented 

 capsule and possesses four pairs of appendages. The first pair are the various 

 shaped feelers (antennae), which are placed on the superior surface of the head next 

 to the eyes ; then more ventrally placed a pair of upper jaws (mandibles) without 

 palpi and without articulations ; they are powerful masticatory organs. 1 The first 

 pair of lower jaws (maxillae) are jointed and bear a palpus (palpus maxillaris) ; the 

 second pair of maxillae are soldered together and form the lower lip (labium), and 

 likewise carry a palpus labialis on each side. The upper lip (labrum), as well as 

 the other parts (which, however, are only appendages), belong to the mouth, which 

 is really formed of a number of closely united pieces. The mouth parts are modified 

 according to the functions required of them. Coleoptera, Neuroptera, and Ortho- 

 ptera have biting or masticatory mouth parts which conform with the scheme 

 described above. In the licking mouth parts of the Hymenoptera the maxillae and 

 under lip are considerably elongated, while the mandibles retain their form 

 and are used for triturating the food ; in the Lepidoptera nearly all the mouth 

 parts are shortened except the maxillae, which form a long and sometimes spirally 

 rolled suctorial proboscis ; the Diptera and Rhynchota have piercing and sucking 

 mouth parts. The mandibles and maxillae are metamorphosed into needle-like 

 structures, while the suctorial apparatus is formed by the labrum. 



The thorax consists of three segments, which are frequently united ; ventrally it 

 carries three pairs of legs, which consist of a definite number of articulated pieces 

 joined together. Their form also changes according to their function, so that legs 

 for running, walking, digging, swimming, jumping, and preying are seen. A pair 

 of wings are respectively attached to the last and last but one thoracic rings, and 

 these may be traced back, not to metamorphosed appendages, but to tracheal 

 branchia. They are composed of chitinous membranes supported by branched 

 structures (veins or ribs). Their size and formation vary ; they are seldom of equal 

 size and form (^europtera) ; often the posterior wings are larger than the anterior 

 wings, the former then only serving as protective coverings for the latter 

 (Coleoptera), or the anterior wings are larger (Lepidoptera}, or the posterior wings 

 are shortened or are entirely absent (Diptera]; and finally there are insects in 

 which both pairs of wings are lacking. 9 



The abdomen retains its segmentation, but, with the exception of a few groups 

 related to the primitive forms of insects, has no appendages in the imago condi- 

 tion ; the abdomen usually consists of ten segments, on the last of which the anus 

 is situated. 



1 [The mandibles are only powerful masticatory organs in biting-mouthed insects 

 (Mandibulatd) ; in the sucking or piercing-mouthed insects they may be absent, or in the 

 form of needle-like stylets (Haiistellata}.. V. T.] 



2 [As in the order Aptera, which includes the Thysanura and Collembola, and also 

 exceptions in other orders, as the fleas amongst Diptera, the Mutillus and ants amongst 

 Hymenoptera. F. V. T.] 



