i^Jn. 



Th^ 



Fig. 41 



, 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, s ; 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, ani^ is separated 

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

 enclosed dorsally. //, head ; M, thorax ; /;-, prociodseum ; 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 ; «, 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 

 antenaary segment (deuto-cerebrum) ; j, ganglion of the intercalary segment 

 (trito-cerebrum) ; ^, 3, 6, ganglia of the mandibles, maxilla;, and labium ; 

 7-/9, thoracic and abdominal ganglia ; ladr^ labrum ; in, mouth ; anf, 

 antennse ; md^ mandibles ; mx^, maxillse ; ?«jr2, labium ; T'Al, prothoracic 

 limb ; adr, first abdominal limb rudiment ; abii^ eleventh abdominal 

 limb rudiment ; an, anus ; T, telson ; sil, the first, and stio, the last stigm^ 

 of the right side. Digitized by Microsoft® 



