iSgO.] ENTOMOLOGICAL NEWS. 7I 



(crabs, lobsters, shrimps, etc.)- It is necessary, therefore, to 

 find some differences which will distinguish the Insects from all 

 other Arthropods.* One of these is the breathing by trachece, 

 which are tubes, composed of thin membranes kept open by a 

 fine, but stiff, wiry thread twisted spirally throughout the whole 

 course of the tubes. The tracheae have their external openings, 

 called spiracles or stigmata, along the sides of the body. From 

 the spiracles the tracheae pass inwards and ramify in all directions 

 throughout the body. The Crustacea breathe by gills, and hence 

 form a division of the Arthropods called Branchiata (from the 

 Greek work brangchia, gills). All other Arthropods than the 

 Crustacea breathe by tracheae, or similar structures, and hence 

 form the division Tracheata. 



(2) The body of an adult insect is divided into three regions, — 

 head, thorax and abdoyneii. Iii the Crustacea and Arachnida, 

 there are, as a rule, two regions, the united head and thorax 

 {cephalo-thorax), and the abdomen. In the Onychophorans and 

 Myriapods the body is worm-like, and can hardly be said to be 

 divided into regions (although, of course, segmented); the head, 

 however, is distinct. 



(3) Insects, when they have attained their imago or perfect 

 form, have one pair oi antenncB (or " feelers") attached to the 

 head, three pairs of legs which are restricted to the thorax, and 

 usually two pairs of wings, also attached to the thorax. The 

 Arachnida have no true antennae, but have four pairs of legs at- 

 tached to the thoracic part of the cephalo-thorax. The Myria- 

 poda and Onychophora have one pair of antennae and numerous 

 pairs of legs. The Crustacea have two pairs of antennae and 

 usually five or more pairs of legs to the thoracic part of the 

 cephalo-thorax, and often some abdominal legs. No other Ar- 

 thropoda than the Insecta have wings, and even some Insects are 

 destitute of them during their entire life. 



With respect to the states or forms assumed in the course of 

 their lives, Insects may be grouped into three divisions : 



I. Insects which pass through four states, viz., (i) the Egg, 

 (2) the Larva (caterpillar, maggot, grub, or " worm"t), (3) the 

 Pupa (chrysalis), usually a quiescent state, and (4) the Imago 

 (perfect insect). 



* The characters given in this paper for the classes of Arthropoda are mainly those used 

 in Claus and Sedguick's excellent Text Book of Zoology. 

 t Such as the " Tomato-worm," " Grape-vine worm," and similar plant-feeders. 



