NO. 2 ENCYCLOPEDIA OF INSECT ANATOMY — SNODGRASS II 



"metamorphosis" of the insect, the true metamorphosis is the change 

 of form the larva has undergone in its independent evolution. (See 

 Metamorphosis.) 



Pupa: The term is taken over from the Latin word for young 

 girl, puppet, baby, or doll. While there is no question as to the ap- 

 plicability of the word, there has been much discussion as to the 

 nature of the pupa. Does it represent the last nymphal instar of an 

 insect without metamorphosis, or is it a preliminary form of the 

 adult? Long arguments have been presented on each side of the 

 question, but it seems that a few pertinent facts will give a sufficient 

 answer. 



Naturally, since the pupa is formed inside the larva, when the 

 larval cuticle is shed the pupa has the elongate form of the larva. 

 On the other hand, the pupa has the imaginal compound eyes and 

 the imaginal mouthparts, legs, and wings in a halfway stage of de- 

 velopment. Clearly, therefore, the young pupa is a preliminary de- 

 velopmental stage of the imago modeled in the larval cuticle. Within 

 the larval cuticle it undergoes a stage of development and reconstruc- 

 tion until when it finally casts off the larval skin it has the typical 

 form of a pupa. Thereafter it does not change in external shape. 



The body of the mature pupa takes on the form of the imago. 

 Thus it serves as a mold for the newly forming adult muscles and 

 allows them to become attached properly on the imaginal cuticle. 

 This alone has been proposed as a theory adequate to explain the 

 pupa as a preliminary adult stage. On the other hand, it has been 

 held that this theory of the pupa involves the unusual occurrence of 

 a moult in the stage of holometabolous insects. But the mayflies 

 moult once after attaining a fully winged condition, and the aptery- 

 gote insects, as well as most other arthropods, moult successively 

 throughout life. Still the pupal moult may be regarded as a second- 

 ary one necessitated by the immaturity of the pupa. Moulting is 

 determined by hormones, and hormones are powerful controlling 

 agents in development. Insect endocrinologists have shown that they 

 can make various adult insects moult again by transplanting into 

 them the appropriate endocrine glands. 



The larval skin containing the young pupa has often been called 

 the "prepupal stage of the larva," but with the moulting of the larval 

 cuticle, not yet cast off, the larval life is ended. The young pupa 

 ensheathed in the larval cuticle has been called the "prepupa," but 

 it is simply a young pupa in a formative stage and still cloaked in 

 the larval skin. It is not distinct from the mature pupa which is ex- 



