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TEXT-BOOK OF ENTOMOLOGY 



cylindrical, nearly motionless, with no appendages, but with a diges- 

 tive canal and a nervous and vascular system (Fig. 652). 



After a second moult the third and last larval stage is attained, 

 and the insect is of the ordinary appearance of ichneumon larvae. 



Not less striking is the life-history of Polynema, which lays its 

 eggs in those of a small dragon-fly (Agrion virgo). The first larval 

 stage is most remarkable. It hatches as a microscopic immovable 

 being, entirely unlike any insect, with scarcely a trace of organiza- 

 tion, being merely a flask-shaped sac of cells. After remaining in 

 this state five or six days it moults. 



- a 



st- 



m at md 



FIG. 650. Development of Platygaster : A, stalked egg: a, central cell giving origin to the 

 embryo. J>, g, germ ; b, blastoderm cells. C, the same, farther advanced. />, cyclops-like embryo : 

 ///'/, rudiments of mandibles ; d, rudimentary pad-like organs, seen more developed in E '; st, bilobed 

 tail. 



The second stage, or Histriobdella-like form, as Ganin names it, 

 is more like that leech-like worm than an insect. 



The third larval form is very bizarre, though more as in insects, hav- 

 ing rudimentary antennae, mouth-parts, legs, and ovipositor. In this 

 condition it lives from six to seven days before pupating (Fig. 653). 



The strange history of another egg-parasite (Ophioneurus) agrees 

 in some respects with that of the foregoing forms. It is when 

 hatched of an oval shape, with scarcely any organs, and differs from 

 the genera already mentioned in remaining within its egg-membrane, 

 and not assuming their strange shapes. From the cylindrical sac- 



