274 MANUAL OF ZOOLOGY. 



ever, 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 metamorphosis, or by the degree 

 of its completeness when present, Insects are divided into 

 sections, called respectively Ametabola, Hemimetabola, and 

 Holometabola, which, though not, perhaps, of a very high scien- 

 tific value, are nevertheless very convenient 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 (Apterd) on escaping from 

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

 and though they may change their skins frequently, they undergo 

 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 locomotive, 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 that 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 

 active condition of the pupa, this kind of metamorphosis is 

 said to be "incomplete." 



In some members of this section however such as the 

 Dragon-flies the larva and pupa are aquatic, whereas the 

 imago leads an aerial life. In these cases there is necessarily 

 a .considerable difference between the larva and the adult ; but 

 the larva and pupa are closely alike, and the latter is active. 



Section 3. Holometabolic Insects. These comprising the 

 Butterflies, Moths, Beetles, &c. pass through three stages 

 which differ' greatly from one another in appearance, the 

 metamorphosis, therefore, being said to be " complete." 

 In these insects (fig. 107) the "larva" is vermiform, seg- 

 mented, and usually provided with locomotive feet, which 



