x PHYLUM ARTHROPOD A 251 



velop into males (drones). In one or two groups, includ- 

 ing the scale insects ( Coccida) , and gall insects ( Cynipidcz} , 

 males are never developed, so that reproduction is exclu- 

 sively parthenogenetic. Ptzdogenesis accompanies parthe- 

 nogenesis in certain of the Diptera or two-winged insects, 

 i.e., the larva produces ova and embryo without impregna- 

 tion. 



The eggs when laid are protected from injury by a num- 

 ber of methods : they may be buried in the earth, or laid in 

 the interior of certain plants or even animals. The deposi- 

 tion of eggs by means of an ovipositor in the leaves or other 

 parts of plants gives rise to swellings galls in the inte- 

 rior of which the young insects are protected and nourished. 

 In the case of many insects the eggs are enclosed in a 

 cocoon ; in others they are enclosed in gelatinous or waxy 

 material. 



In some instances the young insect, when it escapes from 

 the egg, has exactly the form of the parent, except that per- 

 haps the wings have not yet grown. But in most instances 

 there is a metamorphosis. In some this is comparatively 

 slight and gradual, the adult insect differing from the larva 

 only in comparatively unimportant points, and the segments 

 and appendages of the latter becoming directly converted 

 into those of the former. Such a metamorphosis is said to 

 be incomplete. The term complete is applied to the meta- 

 morphosis of the majority of insects, in which the larva 

 differs so completely from the imago, or perfect insect, in 

 external form, the nature of the appendages and the internal 

 organisation, that there is need of a quiescent or pupa stage 

 during which the whole animal, or a considerable part of it, 

 undergoes an entire transformation. The butterflies and 

 moths (Lepidoptera) (Fig. 143) may be taken as a good 

 example of such a complete metamorphosis. The larvae, or 



