214 MANUAL OP ZOOLOGY. 



morphosis,' before attaining maturity. In some Insects, how- 

 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 

 scientific value, are, nevertheless, very convenient in practice. 

 Section 1. Ametalolic 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 

 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, mudh 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 me- 

 tamorphosis, therefore, being said to be 'complete.' In these 

 insects (Jig. 68) the 'larva' is vermiform, segmented, and 



