242 THE EMBRYOLOGY OF THE BLOW-FLY IN THE EGG. 

 \ 



. 38.—/, An Optical Section of an Kmbryo in the stage represented by sections, 

 Figs 3 to 6, PI. XIII. ; .?, A Diagram construcled from Tranverse .Sections. The 

 parts surrountHng the yell< are drawn larger than they really are, so that the yelk 

 is represented by too small a space : am, amnion ; / //, jiortion of the amnial 

 tube which becomes the primitive band ; / n, primitive archenteron ; /, pro- 

 cephalic lobe ; s, serosa ; ///, ///', head-fold. The position of the future slomo- 

 dieum is represented by the dotted line si. The shaded nuclei indicate cells 

 which occupy the median line. The arrow, j', shows the communication Ijctween 

 the folds of the serosa and the yelk ; the second arrow below this shows the 

 opening into the amnial tube in the cephalic region. 



Description oi- Plate XIII. 



The tigures in this plate are all copied from Graber [114]. 



Fig. I.— a section of the egg of a Blow-ny, showing the segmenting morula within 



the yelk (a condition regarded by Graber as abnormal). 

 Fic:. 2.— The posterior pole of the blastoderm of the Ulow-lly in the blastula stage, 



showing the polar cells. 

 I'KJS. 3 to 6. — Four sections of the ovum of the Blowfly in the stage represented by 



The position of these sections is indicated by doited lines in I-ig. 38. 



I'K.. 3 represents a .section taken in the region indicated by line I. 



Fic. 4 represents a section in the region indicated by line 2. 



Flc. 5 represents a section immediately behind the head-fold, hj'. 



Fig. 6 represents a section in the region indicated by line 3. 

 The following refer to all the figures in which they occur : 

 (I, archenteron ; am, amnion ; /; /, head-fold ; and me, calomic sac. 



