1890.] ENTOMOLOGICAL NEWS. 7 1 



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

 find some differences which will distinguish the Insects from all 

 other Arthropods/ 1 ' One of these is the breathing by trachca\ 

 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 trachea- have their external opening, 

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

 the spiracles the trachea- pass inwards and ramify in all direction- 

 throughout the body. The Crustacea breathe by ^ills, and hence 

 form a division of the Arthropods called Branchiata (from the 

 < ircek work brangchia, gills). All other Arthropods than the 

 Crustacea breathe by tracheae, or similar structures, and henci- 

 form the division Trachea ta. 



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

 head, thorax and abdomen. In the Crustacea and Arachnida, 

 tin-re 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 (^antenna; (or " feelers") attached to the 

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

 usually two pairs ot 'Beings, also attached to the thorax. The 

 Arachnida have no true antenna-, 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 antenna- and 

 11 nally 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, vi/., ( i ) the r.gg, 

 (2} the Lann i caterpillar, ma^"t, ^rub, or " worm" i >, 3) the 

 Pwpa (chrysalis), usually a quiescent state, and (4) the Im 

 (perfect insect). 



* The characters given in this paper for thi classi > Irthropoda are mainly thos 



in i 'l.uis anil Si-ili;\\ ick'si-M'i-lli-nt I i-\t 1'unk <>t /n. ' 

 t Such as the " Tomato-worm," " < Irapo-vinv wui in." and similar pl.int-lcr 



