THE METAMORPHOSIS OF INSECTS 191 



Obtected pupa. Pupag which like the pupae of Lepidoptera, have 

 the limbs glued to the surface of the body, are termed obtected pupae. 



C oar date Pupa. Pupae that are enclosed within the hardened 

 larval skin, as is the case with the pupae- of most of the Diptera, are 

 termed coarctate pupae. 



The imago The fully developed or adult insect is termed the 

 imago. 



The life of the imago is devoted to making provision for the 

 perpetuation of the species. It is during the imaginal stadium that 

 the sexes pair, and the females lay their eggs. With many species 

 this is done very soon after the last ecdysis ; but with others the egg- 

 laying is continued over a long period; this is especially true with 

 females of the social Hymenoptera. 



h. HYPERMETAMORPHOSIS 



There are certain insects, representatives of several different orders 

 that exhibit the remarkable peculiarity in their development that the 

 successive larval instars represent different types of larvae. Such 

 insects are said to undergo a hypermetamorphosis. 



The transformations of several of these insects will be described 

 later in the accounts of the families to which they belong; and for 

 this reason, in order to avoid repetition, are not discussed here. The 

 more striking examples are Mantispa, Meloe, Stylops, and Platy- 

 gaster. 



I. VIVIPAROUS INSECTS 



There are many insects that produce either nymphs or larvas 

 instead of laying eggs. Such insects are termed viviparous. This 

 term is opposed to oviparous, which is applied to those insects that lay 

 eggs that hatch after exclusion from the body. 



It has been pointed out in the discussion of the reproductive organs that, from 

 the primordial germ -cells, there are developed in one sex spermatoza and in the 

 other eggs; and it should be borne in mind that the germ-cells produced in the 

 ovary of a female from the primordial germ-cells are eggs. These eggs grow and 

 mature; in some cases they become covered with a shell, in others they are not 

 so covered ; in some cases they are fertilized by the union of a spermatozoan with 

 them, and in others they are never fertilized; but in all these cases they are eggs. 

 We may say, therefore, that all insects are developed from eggs. 



A failure to recognize this fact has introduced confusion into entomological 

 literature. Some writers have termed the germ -cells produced by agamic aphids 

 pseudova or false eggs. But these germ-cells are as truly eggs as are those from 

 which the males of the honeybee develop; they are merely unfertilized eggs. 

 The term pseudovum conveys a false impression; while the phrase, an unfer- 

 tilized egg, clearly states a fact. 



