THE CLASS OF INSECTS. 



Fiic. 5. 



stages, from the time of tlioir exclusion from the egg, until 

 they p:iss into mature life. A more careful study of this 

 l^eriod than we ai-e now able to enter upon would show us how 

 much alike the young of all Arthropods are at first, and how 

 soon tliey begin to difter, and assume the shape characteristic 

 of their branch. 



Most Worms, after leaving the egg, are at first like some 

 infusoria, being little sac-like animalcules, often ciliated over 

 nearly the entire surface of the infinitesimal body. 

 Soon this sac-like body grows longer, and con- 

 tracts at intervals ; the intervening parts become 

 unequally enlarged, some segments, or rings, 

 formed b}^ the contraction of the body-walls, 

 greatly exceeding in size those next to them ; and it thus 

 assumes the appearance of being more or less equally ringed, 

 ^, as in the young Terebella (Fig. 5), wdiere the 



ciliix^ are restricted to a single circle surrounding 

 the body. Gradually (Fig. G) the cilia? disap- 

 pear and regular locomotive organs, consisting 

 of minute paddles, grow out from each side ; 

 feelers (antenuie), jaws, and eyes (simple rudi- 

 mentary eyes) appear on the few front rings 

 of the body, which are grouped by themselves 

 I into a sort of head, though it is difficult, in a 

 large proportion of the lower worms, for un- 

 skilled observers to distinguish the head from 

 the tail. 



Thus we see throughout the growth of the 



worm, no attempt at subdividing the body 



into regions, each endowed Avith its peculiar 



I ^functions ; but only a more perfect system of 



. ' rings, each relatively very equally developed, 



in the figure, also to the dorsal vessel (c), the intestine (6), and the nervous cord (a). 

 The tracheie and a nervous lilameut are also sent into the legs and to the wings. 

 The tracheie are also distrihuted to the dorsal vessel and intestine by numerous 

 bi'anches which serve to hold them in place. — Original. 



Fig. .'). Young Tercheila, .soon alter leavmg the eg^. — From A. Af/assiz. 



Fi(i. (i repre.-^ents the oinl>ryo of a worm (Autolijlus corniitu.-!) at :i later stage 

 ol' growth, n is the middle tentacle of tlie head ; c, one of tlie posterior tentacles; 

 /), the two eye-spots at the base of the huider pair of feelers; c is one of a row of 

 car-like organs {cirri) at the base of which are inserted the locomotive bristles, 



