C26 KNOWER. [Vol. XVI. 



smaller by repeated divisions, while those of the serosa are now 

 comparatively very large, having before this practically ceased 

 to divide. This transparent Q.^g also shows the few large 

 yolk-cells, seen better in sections. 



The growth of the embryo, from the time when the amniotic 

 cavity is completely closed, is chiefly at its posterior end. The 

 hind end of the embryonic band pushes back over the posterior 

 end of the yolk-mass, just beneath the serosa (PL XXXI, Figs. 



25, 27, and 29), while the head end remains fixed. (In some 

 exceptional eggs the embryo is found out of its usual position, 

 slipped forward or backward.) This growth continues for some 

 time over the posterior pole, no marked change being apparent 

 superficially, except an increase in length and breadth. The 

 anterior end, however, becomes gradually less pointed. 



A germ-band slightly older than that shown in PI. XXXI, Fig. 

 24, while not yet one-half the length of that in PI. XXXI, Fig. 



26, would have already acquired a square, broad anterior end, as 

 in the later stage. 



The embryo in PI. XXXI, Fig. 26, is not in the usual position 

 at this period, some few eggs thus exhibiting the germ-band 

 entirely on the ventral surface, and giving its shape and rela- 

 tions better than can be shown by drawing an embryo dissected- 

 off from the yolk. PL XXXI, Fig. 27, represents in side view 

 this same stage, as it is found usually, with the few exceptions 

 just noted. 



The germ-band now continues to push back around the yolk- 

 mass, until about one-third up on the flattened dorsal side of 

 the Q.g%, when the embryo forms a 6^-shaped figure, lying over 

 the enlarged end of the yolk (PL XXXI, Fig. 29). At this time 

 the band is still unsegmented. Posteriorly it terminates in a 

 rounded extremity. The anterior end has in the mean while 

 undergone considerable change. From being a narrow-pointed 

 tip to the band (PL XXXI, Fig. 24), it first gradually widened into 

 a square end (PL XXXI, Fig. 26, and stages between this and PL 

 XXXI, Fig. 24), and finally spread out over the yolk anteriorly 

 and laterally, until now (PL XXXI, Figs. 28 and 29) this region 

 has become the most prominent part of the embryo. Anteri- 

 orly, just in front of the point where the mouth is to appear. 



