474 



ARTHROPODA. 



Increase in the differences of environment and the correlated 

 increase in larval characters lead to complete metamorphosis. In 

 order to profit as much as possible by its adaptation to its environ- 

 ment the larva retains its shape as long as possible ; the gradual 

 change is suppressed and the alteration in form necessary to the 

 metamorphosis is postponed until the end of the larval life, to the 

 period between the last two molts. In this interval there is such 

 .an energetic transformation of the organism that the performance 

 of ordinary vital functions, especially motion and feeding, is in- 

 terfered with or rendered impossible. This last stage therefore 

 becomes a period of rest, the pupal stage, upon the existence of 

 which great weight must be laid in the definition of complete met- 

 amorphosis. The more complete the condition of rest the more 

 pronounced is the holometabolous development. From this point 

 of view different types of pupae are distinguished : pupae liberae, 

 pupae obtectae, and pupae coarctatae. In a free pupa (pupa libera) 

 the appendages stand out from the body (fig. 500), so that not 



FIG. 500. Larva and pupa of May beetle, a', a", fore and hind wings ; an, anus ; 

 at, antennae; o, eyes; p'-p'", legs ; s, spiracles. 



only the segmentation of the body but the antennae, legs, wings, 

 and often the mouth parts of the imago are visible. Such pupae 

 have a certain power of motion, as, for instance, the pupae of many 

 Neuroptera and mosquitos, the latter rising and falling in the 

 water. The covered pupae (pupae obtectae) at the moment of 

 pupation have free appendages which with the hardening of the 

 chitin become closely appressed to the body, so that even by close 

 inspection only indistinct contours can be seen (fig. 501). Motion 

 is confined to bending of the whole body, as is familiar in the 

 pupae of moths and butterflies. The pupae coarctatae are without 

 motion because here the pupa (in structure a pupa libera) is en- 

 closed in a larger coat, the last larval skin (Muscajia). 



The variations among larvae are even greater than with pupae. 

 Here structure and jointing of the body are so completely under 

 the influence of environment that with similar or different con- 



