ANNULOSA: INSECTA. 34! 



The antennae are movable, jointed filaments, attached usually 

 close to the eyes, and varying much in shape in different 

 Insects. They doubtless discharge the functions of tactile 

 organs, but are probably the organ of other more recondite 

 senses in addition. 



The sexes in Insects are in different individuals, and most 

 are oviparous. The ovum undergoes partial segmentation ; 

 and the embryo has its future ventral surface turned outwards, 

 and its dorsal surface inwards. Generally speaking, the young 

 insect is very different in external characters from the adult, 

 and it requires to pass through a series of changes, which con- 

 stitute the "metamorphosis," before attaining maturity. In 

 some Insects, however, there appears to be no metamorphosis, 

 and in some the changes which take place are not so striking 

 or so complete as in others. By the absence of metamor- 

 phosis, or by the degree of its completeness when present, 

 Insects are divided into sections, called respectively Ameta- 

 bola, Hemimetabola, and Holometabola, which, though not, per- 

 haps, of a very high scientific value, are nevertheless very con- 

 venient in practice. 



Section i. Ametabolic Insects. These pass through no meta- 

 morphosis, and also, in the mature condition, are destitute of 

 wings. The young of these insects (Aptera) on escaping from 

 the ovum resemble their parents in all respects except in size ; 

 and though they may change their skins frequently, they under- 

 go no alteration before reaching the perfect condition, except 

 that they grow larger. 



Section 2. Hemimetabolic Insects. In the insects belonging 

 to this section there is a metamorphosis consisting of three 

 stages. The young on escaping from the ovum is termed the 

 "larva;" when it reaches its second stage it is called the 

 " pupa," or " nymph ; " and in its third stage, as a perfect 

 insect, it is called the "imago." In the Hemimetabola, the 

 " larva," though of course much smaller than the adult, or 

 " imago," differs from it in little else except in the absence of 

 wings. It is active and loconjotive, and is generally very like 

 the adult in external appearance. The "pupa," again, is a 

 little larger than the larva, but really differs from it in nothing 

 else than in the fact tl^it the rudiments of wings have now 

 appeared, in the form of lobes enclosed in cases. The " pupa " 

 is still active and locomotive, and the term " nymph " is usually 

 applied to it. The pupa is converted into the perfect insect, 

 or " imago," by the liberation of the wings, no other change 

 being requisite for this purpose. From the comparatively small 

 amount of difference between these three stages, and from the 



