Fig. 41 



A, />, 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 i>p is the ventral plate. B shows the for- 

 mation of the amniotic folds, j ; 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 ; tk, thorax ; pr, proctodaeum ; y, yolk. E. A 

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

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

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

 lowest figure is 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, 3, 6, ganglia of the mandibles, maxillae, and labium ; 

 7-79, thoracic and abdominal ganglia; labr, labrum ; vi, mouth; ant, 

 antennas ; md, mandibles ; m.r l , maxillae ; mx*-, labium ; 7 1 /* 1 , prothoracic 

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

 limb rudiment ; an, anus ; T, telson ; stl, the first, and stio, the last stigma 

 of the right side. 



