224 HAROLD R. HAGAN 



The egg. The egg is elongate-oval, with an evenly rounded 

 posterior end and tapering slightly to a somewhat smaller, more 

 pointed anterior end. The shape is generally cylindrical but 

 the anterior end is usuall}^ a little compressed laterally due to 

 the pressure of the adjoining eggs in the ootheca. Distinct 

 though not strongly concave and convex surfaces denote the 

 dorsal and ventral surfaces respectively. A prominent button- 

 shaped micropyle almost covers the anterior end of the egg. 

 The length averages 4.5 mm. and the diameter near the middle 

 of the longitudinal axis is about 1.3 mm. 



The emhryonic rudiment. The ventral plate is remarkably 

 short when compared with the size of the egg. It varies, ac- 

 cording to a number of measurements, from 0.46 mm. to 0.59 

 mm. in diameter. In surface view it consists of a sharply de- 

 fined circular area of closely compacted cells on the ventral side 

 of the egg, about two-thirds the distance from the anterior pole. 

 When the egg is viewed from the lateral aspect this area appears 

 flattened or even as a very slight depression in the yolk. 



After gastrulation the germ band elongates rapidly, involving 

 the entire ventral plate; the anterior end develops laterally also 

 to form the rudiments of the cephalic lobes, while the posterior 

 end assumes a lengthened form, giving the whole a shape roughly 

 suggesting the letter T (fig. 1). The antero-posterior axis of the 

 germ band corresponds with the same axis of the egg and lies in 

 the same direction. The anterior end of the embryo is directed 

 toward the anterior end of the egg throughout its entire embryonic 

 history. On arriving at this stage, however, the embryonic 

 rudiment undergoes successively a number of intermediary steps. 

 The first change noticed is the lengthening of the circular or 

 slightly oval ventral plate with apparently a slight contraction 

 of its width. This movement is accompanied by activity in the 

 antero-lateral region where the cephalic lobes are beginning 

 their development. The ventral plate at this point appears 

 somewhat U-shaped in outline, the base of the U corresponding 

 to the posterior end. This appearance is quickly passed because 

 of the continued elongation of the germ band and the active 

 growth and extension of the rudiments of the cephalic lobes. 



