STRUCTURE OF INSECTS. 17 



of its growth it is termed a larva, but the state immediately pre- 

 ceding that in which it assumes its final or imago form is termed the 

 pupa. The variations in the form of these several states in the 

 different orders have been employed in the construction of the meta- 

 morphotic distribution of insects, to be subsequently noticed, which 

 will render it unnecessary to enlarge upon them at any great length 

 in this place. Insects, in respect to the relation of the larva with the 

 imago, may be divided into two principal divisions which I have 

 termed Heteromorpha, or those in which there is no resemblance 

 between the parent and its offspring; and ^^^morpha, or those in 

 which the larva resembles the imago, except in the absence of wings. 

 In the former the larva is generally worm-like and articulated in its 

 form, of a soft and fleshy consistence, and furnished with a mouth, and 

 often with six short legs attached in pairs to the three segments 

 succeeding the head. In the latter, including the Orthoptera, He- 

 miptera, Homoptera, and certain Neuroptera, the body, legs, and 

 antennae are nearly similar in their form to those of the perfect insect, 

 but the wings are wanting. 



The Period of the Larval State is that in which the operations of 

 feeding are especially carried on, and during which, owing to the rapid 

 growth of the insect, whereby the outer envelope from time to time 

 becomes too small for the creature, it is necessary that a succession 

 of moultings should take place. When, however, the insect has at- 

 tained its full size as a larva it ceases feeding, prepares for itself 

 a retreat formed of various materials, but often composed of silk 

 drawn from the spinnerets of the lower lip, and which is termed a 

 cocoon. Within this retreat the insect again throws off its skin and 

 appears as a pupa or chrysalis, in which the rudiments of the limbs 

 of the imago are more or less distinctly seen. In the Sa^omorphous 

 division, however, the pupa continues active, differing only from the 

 larva in its increased size, and in having attained short rudimental wing- 

 cases upon the back of the mesothoracic and metathoracic segments. 



The Pupa is far more variable in its form in the different primary 

 groups than the larvae ; and hence Fabricius * employed the cha- 

 racteristic name of the variation of the pupa to designate the general 

 nature of the metamorphosis, whereby the metamorphosis of an insect 

 is incorrectly said to be incomplete in Scarabacus and Apis, M'here the 

 larva is quite unlike its parent, and the pupa pedate, but quiescent ; 



* Philosophia Entomologlca, p, 5Q. § 6. 

 C 



