MYUIAPODA. 



227 



forward, being situated in the vicinity of the head, between the 

 first and second segments ; the sexes, however, as in insects, are 

 perfectly distinct, and the conformation of the internal organs 

 coincides with that type of structure which is common to the insect 

 orders. 



(271.) Another important distinction between these animals and 

 insects properly so called, is met with in the mode of their growth 

 and developement. Insects, as we shall more fully explain here- 

 after, undergo a more or less complete change in their outward 

 form as they advance through several preparatory stages to their 

 mature state : during the progress of these changes, which consti- 

 tute what is usually called the metamorphosis of insects, they are 

 invariably unable to perpetuate their species ; and it is only in their 

 last or perfect condition, which is ordinarily of very short duration, 

 that the sexual organs attain their perfect developement, and are 

 fit for reproduction. In this state all true insects have six legs, 

 which is one of the most important characters of the class. The 

 Myriapoda, likewise, undergo several changes of form as they ad- 

 vance to maturity ; but these changes principally consist in the 

 repeated acquisition of additional legs, so that in their perfect 

 condition, instead of the limited number of six legs met with 

 in insects, these organs have become extremely numerous. The 

 progress of these transi- Fig. 99. 



tions, from their imma- 

 ture to their fully de- 

 veloped state, has been 

 well observed by De 

 Geer * and Savi ;*f and 

 the result of their ob- 

 servations is here given, 

 in order that the rea- 

 der may compare the 

 different steps of the 

 process with what we 

 shall afterwards meet 

 with in the more highly 

 organized articulata. 



The eggs, (Jig. 99, 



* Memoires pour servir a 1'Histoire des Insectes. 7 vols. 4to. Stockholm, 1778. 

 t Osservazione per servire alia storia di una specie di Julus communissima. Bo- 

 logna, 1817. 



