288 INSECTA. 



now commences laying eggs, and, during the process, the abdomen 

 exhibits a continual undulatory motion, produced by the peristaltic 

 movement of the egg-ducts ; while the workers convey away the 

 eggs as they are laid, and deposit them in the distant rearing-cells 

 of their wonderful habitation. The reader will be able to form 

 some idea of the relative proportions and outward appearance of 

 the edifices erected by these comparatively minute beings by the 

 group of their citadels represented in the back-ground of the figure ; 

 but to describe them more minutely would lead us into details 

 unconnected with our subject.* 



(335.) The eggs of these little animals vary much in shape and 

 external configuration ; so that, from the beauty of their forms and 

 exquisite sculpture, some of them are interesting objects for the 

 microscope. 



(336.) We have already spoken concerning the metamorphosis 

 which insects undergo during the progress of their developement from 

 the form under which they first leave the egg to their mature con- 

 dition, when they become fertile, and, in most instances, acquire 

 those instruments of flight so generally characteristic of their perfect 

 state. Before entering upon a more minute inquiry concerning 

 the physiological principles upon which the important changes in 

 question depend, and the phenomena attending the process, it will 

 be advisable to cite a few more examples illustrative of the most 

 interesting varieties of metamorphosis signalized by authors. Fa- 

 bricius distinguishes five different kinds of metamorphosis, and has 

 applied a different name to each. 



The first class comprises all insects of which the larva is a mag- 

 got entirely deprived of legs, that after having changed its skin, or 

 moulted, a certain number of times, becomes, previous to its last 

 change, incased in an oval horny sheath, or pupa-case, whereon not 

 the least trace of the limbs of the mature insect is to be detected ; 

 such pupse are absolutely without the power of motion, and are 

 distinguished by the name of coarctate : examples of this sort of 

 metamorphosis are met with in the common house-flies (Muscida), 

 and the forms of their larvae and pupse are familiar to every one. 



Of the second kind, technically named obtected, the Lepido- 

 ptera furnish well-known instances. The changes which occur in 

 the developement of the silkworm, represented in the annexed 

 figure (Jig- 131), may readily be witnessed. In such insects the 

 full-grown caterpillar, having enclosed itself in a silken ball, throws 



* Vide Smeathman, Phil. Trans, vol.lxxi. 1781. 



