PARTS OF INSECTS, 21 



DEFINITION OF INSECTS. 



Iksects are so called because they are divided into numerous seg- 

 ments ; and not from their being almost separated into two parts, which 

 are merely attached to each other by a slender thread, as is generally 

 supposed. 



AH genuine insects have six legs; a head distinct from their body, 

 and furnished with two antenuce or horns; and have pores conducting 

 to tracheae arranged along their sides for respiration : they are all pro- 

 duced from eggs. Some undergo no metamorphosis, others but a par- 

 tial change, whilst the remainder pass through three stages of exist- 

 ence, after being hatched from tlie egg. 



PARTS OF INSECTS. 



An insect may be divided into four parts. 

 1. Caput. 2. Truncus. 3. Abdomex. 4. Artus. 



CAPUT, the Head, which is distinguished in most insects, is fur- 

 nished with Ei/cs, uintennce, and a Mouth. 



Eyes. Many insects have two crescents or immoveable caps, com- 

 posing the greatest part of their head, and containing a prodigious 

 number of little hexagonal protuberances, placed with the utmost re- 

 gularity and exactness in lines crossing each other and resembling lat- 

 tice-work : these are termed compound eyes. 



Leeuwenhoek reckons in each eye of the Libellula, or Dragon-fly, 

 12,544 lenses, or in both 25,088; the pictures of objects painted 

 thereon must be millions of times less than the images of them pic- 

 tured on the human eye. There is no doubt tliat insects still smaller 

 have eyes adapted to discern objects some thousands of times less than 

 themselves ; for so the minute particles they feed on must certainly 

 be. Besides these larger eyes, many insects have three small s})heri- 

 cal bodies placed triangularly on the crown of the head, called ocelli or 

 stemmata (Pi. 10. Jig. 11. b). They are simple, and made for viewing 

 large and distinct objects ; the other eyes for small and near ones. 



Antenna. The antenna are two articulated moveable processes 

 placed on the head : they are subject to great variety, and were the parts 

 from whence Linne formed his genera : they are called 



Setaceous, when they gradually taper towards their extremity; 



Clavated, when they grow gradually tliicker from their base; 



Tiliform, of an equal thickness throughout the whole of their length"; 



Moniliform, formed of a series of knots, resembling a string of 

 beads ; 



Capitate J when they terminate in a knob; 



