ZOOLOGY. 



with the female element in the process of repro- 

 duction. Spiders are oviparous, but undergo no 

 metamorphoses. 



CLASS 3. Myriapoda have the head distinct, 

 bearing a pair of antennae, and usually a number 

 of simple eyes. The thorax is united with the 

 abdomen, the whole being divided into a large 

 number of similar segments, each furnished with 

 one or two legs on each side. They respire by 

 tracheae. 



ORDER i. Chilopoda, in which the number of 

 joints composing the antennae is never less than 



fourteen. Litho- 

 bius fordpatus, a 

 British species, is 

 about two inches 

 in length, and 

 quite harmless ; 

 Lithobius forcipatus. but some of the 



Scolopendra, well 



known as Centipedes, found in hot climates, are 

 powerful and predaceous, and sometimes measure 

 one foot in length. 



ORDER 2. Chilognatha, in which the antennae 

 are composed of only seven joints. It includes 

 the vegetable-eating Millepedes (lulus), charac- 

 terised by the great number of the legs. The 

 familiar Gally-worm (Polydesmus) is another ex- 

 ample. 



CLASS 4. Insecta are articulate animals, in 

 which the body is divided into three distinct 

 regions the head, thorax, and abdomen. The 

 head carries the antennas or feelers ; the legs, 

 six in number, being borne by the thorax ; while 

 the abdomen is destitute of jointed appendages. 

 They breathe by tracheae, and are generally fur- 

 nished with wings attached to the thorax. 



Considering the vast number and variety of 

 insects that are found everywhere upon the earth, 

 with their diversity of habits and structure, it must 

 suffice here to point out the main characters of the 

 class, merely mentioning some of the most im- 

 portant families. Indeed, the subject is so vast, 

 that it is studied as a distinct branch of Zoology, 

 under the term Entomology. 



The body is never composed of more than 

 twenty segments, which have usually a horny or 

 chitinous investment, forming an exo-skeleton, to 

 which the muscles are attached. The segments 

 are united to each other by a membranous skin, 

 thus giving flexibility to the whole. The seg- 

 ments of the head are united into a single piece, 

 which bears the antennae, the eyes, and organs of 

 the mouth. The mouth is variously modified, ac- 

 cording as it is suited for biting, for suction, or for 

 both combined. In Masticat- 

 ing or Biting insects, such as 

 Beetles, the mouth consists of 

 six separate organs (see fig.), 

 (i) An upper lip (labrum, /i) 

 attached to the under surface 

 of the head ; (2) A pair of 

 horny biting jaws (mandibles, 

 mm) ; (3) A pair of chewing 

 jaws (maxillae, mx), bearing 

 one or more pairs of ' maxil- 



iur~, fi, f o -Rootio lary palpi' ( m P}\ an d a lower 

 Mouth of a Beetle. .. v, r ,. r /-S i > 



lip (labium, (2) also bearing a 



pair of palpi (lp}. The typical suctorial mouth, 

 10 



as seen in the Butterflies, consists of a long 

 trunk, which, when at rest, is coiled up in a 

 spiral form beneath the head. It represents the 

 maxilla?, which, coming together, form a tube, 

 through which the juices of the flowers are sucked 

 up. The maxillary palpi are very small, and the 

 labrum and mandibles are rudimentary. The 

 labium, though very minute, bears two large 

 palpi, forming the hairy cushions between which 

 the trunk is coiled up when at rest. In the Bee, 

 the parts are modified partly for biting, and 

 partly for suction. The labium and maxillae are 

 elongated, the latter constituting a sheath which 

 incloses the elongated tongue, thus forming a 

 tubular organ, quite incapable of being coiled up, 

 and through which fluid nutriment is sucked. 

 The mandibles and labium retain their ordinary 

 form. In Bugs and their allies, the labium forms 

 an elongated tubular sheath, inclosing four bristle- 

 shaped organs, which are the modified mandibles 

 and maxillae. The labium of the House-fly is 

 lengthened and grooved on its upper surface. 

 This groove receives the modified mandibles and 

 maxillas in the form of bristles and lancets, which 

 are used for penetrating the skin and sucking the 

 blood of other animals. 



The thorax is composed of three segments, 

 which are named from before backwards, pro- 

 thorax, meso-thorax, and meta-thorax. Each 

 of these bears a pair of jointed legs. The latter 

 two segments also usually carry a pair of wings 

 each. The legs are composed of several joints, 

 named the coxa, trochanter, femur, and trasus. 

 The wings are variously modified in the different 

 orders, and consist of a double membrane, which 

 is supported by hollow tubes or ' nervures,' which 

 ramify in every direction, and contain processes 

 of the tracheae, and passages for the circulation. 

 The abdomen is composed typically of nine seg- 

 ments, though these never carry legs. Some 

 appendages connected with the generative function, 

 or for leaping, for offence or defence, may, how- 

 ever, be connected with it. The digestive system 

 in insects consists of a mouth leading into a gullet, 

 which opens into a ' crop.' From this, in Mas- 

 ticating Insects, it leads into a ' gizzard,' furnished 

 with horny plates. This gizzard leads into the 

 true stomach, continued into the intestine, which 

 terminates in a 'cloaca,' common to it and the 

 generative organs. Salivary and other glands are 

 present, but no absorbent system. The heart is 

 placed dorsally, and consists of several sacs, which 

 open into each other from behind forwards. The 

 circulating fluid enters at the posterior extremity 

 of the so-called ' dorsal- vessel,' and is propelled 

 forwards by it, escaping anteriorly, and passing 

 amongst the tissues, and, as it were, bathing them, 

 for no true veins or arteries have been detected 

 in the bodies of insects. In its course it is aerated 

 by being exposed to the air contained in the 

 tracheae, which ramify throughout the body. The 

 nervous system exhibits the typical annulose 

 plan, and is placed ventrally. The eyes are 

 usually compound that is, they consist of multi- 

 tudes of simple eyes, each of which receives a 

 nervous twig. The eye of the house-fly has four 

 thousand of these simple eyes. Insects are dis- 

 tinguished beyond all other animals by their 

 powers of locomotion, and the perfection of 

 their instinctive actions. The antennae seem 

 to be organs of touch. Insects are unisexual. 



Ui 



