in. 



Fig. 41 



A , B, C, D. Diagrammatic longitudinal vertical sections through an insect egg 

 at different stages of development. In A the yolk is seen surrounded by a 

 single layer of blastoderm cells ; at vp is the ventral plate. B shows the for- 

 mation of the amniotic folds, am ; the ventral plate is segmented and consists 

 of an outer layer of epiblast and a deeper layer. In C the amniotic folds 

 have coalesced below the ventral plate, and the amnion, am, is separated 

 from the serosa. In D the limb rudiments are present, and the yolk is nearly 

 enclosed dorsally. /i, head ; ik, thorax ; pr, proctodauum ; y, yolk. E. A 

 transverse section through the body of an insect embryo, after HeuTer. 

 am, amnion ; s, serosa ; ep, epiblast ; tr, tracheal involution ; , nerve cord ; 

 mes, mesoblastic somite with cavity ; hy, hypoblast ; y, yolk. The lowest 

 figure is a ventral view of an advanced insect embryo, after Heymons. 

 /, the ganglion of the cephalic lobes (proto-cerebrum) ; 2, ganglion of the 

 antennary segment (deuto-cerebrum) \3, ganglion of the intercalary segment 

 (trito-cerebrum) ; 4,5, 6, ganglia of the mandibles, maxillae, and labium ; 

 7-/9, thoracic and abdominal ganglia ; labr, labrum ; ;//, mouth ; ant, 

 antennae; md, mandibles; "/.r 1 , maxillae ; ;.r 2 , lal^ium ; Tli^, prothoracic 

 limb ; abi, first abdominal limb rudiment ; abi i , eleventh abdominal 

 limb rudiment ; an, anus ; 7', telson ; sti, the first, and stio, the last stigma 

 of the right side. 



