346 



THE AGRICULTURAL NEWS. 



October 30, 1909. 



INSECT NOTES. 



NATURAL HISTORY OF INSECTS. 

 Part I. Intkoduutiox 



The animal kingdom is divided into sever.il great groups, 

 or sub-kingdoms, in each of which tlie members have some 

 points in common. The member.s cf diff.rL-u' gi-ou[H have 

 more i>oints of difference than of likeness. 



iivfu t!i'; name 



better, 



:\rlhro- 

 jiiinted 



One of these grou[)3 has bee 

 jjoda which means ' jointed feet ', or perlun 

 limbs '. 



The arthropods are all alike in having j'unted limbs, and 

 they also have other points of likeness. They have bodies 

 that are jointed, or at least that are easily separable into 

 regions or sections, such as head, thorax (the middle body) 

 and abdomen ; or head and hind-body ; or cephalothorax, head 

 and thorax fused together, and abdomen. Arthropod.* have 

 an exo.skeleton of a hard, tir.m substance, known as chitin, to 

 which muscles are attached on the inside, and which protects 

 all the soft and delicate organs. 



The arthropods in their turn are divided into four classes 

 as follows : — 



Crustacea— Crabs, Lobsters, etc. 



Araneida — Spiders, Mites, Scorpions, etc. 



^[yriapoda — Centipedes, Millipedes, etc. 



Hexapoda — Insects. 



Crustacea are to be included crabs, lobsters, 

 shrimps, barnacles, etc., many of which are familiar objects in 

 most parts of the West Indies. Fig. 38 represents the wood- 

 louse, or sow-bug, one of the crustaceans. The crustaceans 

 are mostly aquatic; a few live in damp situations such as 

 damp soil" or decaying vegetable matter. They breathe by 



Class I. 

 „ II. 

 „ III. 



„ IV. 

 Among the 



Eig. 38. Wood-louse. 



Fig. 39. Red Spiuki;. 



means of gills, the head is provided with two pairs of 

 antennae, the abdomen has appendages which are used in 

 locomotion, and the eyes are usually compound, sometimes 

 stalked. The body is divided into two regions, the cephalo- 

 thorax and the abdomen. The cei)halolhorax is composed of 

 the head and the thorax fused together, and is often protected 

 by a iiard shell, the caraiiace. Tlu^ exoskeleton of cliitin is 

 often impregnated with large quantities of lime. 



The Class Araneida includes the spider.s, mites, ticks 

 and scorpions. Fig. 39 shows one of the red spiders, a mite 

 of this class which is sometimes injurious to plants. 

 These animals breathe by means of air tubes (tracheae), 

 or air sacs. Certain species, mites especially, have the 

 entire surface of tlie body adapted for respiration. In 

 the case of most members of this group, the h(!ad 



and thorax are fiised to form a cephalothorax, and the eyes 

 are simple. 



The ;\Iyria|)oda, Class III, include the centipedes and the 

 millipedes (Fies. 40 and 41). These are elongate animals 

 with segmented bodies and jointed limbs and appendages. 



Fig. 40. Ckntii'ede. 



Fig. 41. Millipede. 



The head is distinct from the rest of the body, but the 

 thorax and the abdomen do not differ in structure. The 

 hind body is generally provided with legs its entire length, 

 one or two pairs to each segment. 



Fig. 42. Silver Fish. 



Class IV are the Hexapoda, or true insects. Tlie 

 name Hexapoda means having six legs, and this expresses 

 one of the most distinguisliing characters of the insect. 

 In addition to being artliropods having six leg.s, insects 

 are to be distinguished from others of the group by the 

 following features. The insect body is readily separable 

 into three definite regions — head, thorax and abdomen, and 

 the adult is usually winged. The normal number of wings 

 is two pairs, but it sometimes happens that one, or even 

 both, pairs of wings are wanting, as in the silver tish 

 (Fig. 42). 



