404 Journal of Agricultural Research voi. iv. No. s 



all of which were cut at the same angle, in this way rendering the con- 

 tinuity more uniform and more easily apparent. The following discus- 

 sion chiefly relates to the revolution of the embryo, which for reasons 

 already given it was impossible to include in the previous publication. 



As the embryo starts from the yolk it approaches the posterior pole 

 of the egg until the amnion in the dorso-cephalic region comes in contact 

 with the serosa, as shown in Plate LIX, figure i, of this paper. These 

 membranes then unite and the embryo moves forward slightly, as in 

 Plate VII, figure 2} 



When the amnion and serosa are in contact, the central cavity of the 

 polar organ still opens upon the surface of the egg. This cavity is filled 

 with some substance that does not take the stains so far used. It is at 

 this time that it is very difficult to remove the shell without also removing 

 the contents of the cavity en masse, as they appear to adhere to the 

 shell. In later stages the cavity is empty and has no opening upon the 

 surface of the egg. From this it would appear that the polar organ does 

 act in an excretory capacity and that its entire contents are eliminated 

 when the embryo begins its revolution, and that it ceases to function 

 after this time. 



Figure 3 (PI. LIX) is slightly more advanced, and it is very apparent 

 that the embryo is starting its revolution. The greater portion of the 

 yolk has now collected at the opposite pole of the egg, and the mesenteron 

 is complete throughout. 



Figures 4 and 5 (PI. LIX) represent the embryo much crumpled and 

 folded upon itself in the act of making its revolution, occupying the 

 entire posterior part of the egg, the yolk having collected in the anterior 

 region. The polar organ is migrating backward. Figure 6 (PI. LIX) 

 illustrates the embryo after the turn is completed, and the polar organ 

 is on the opposite side of the e.gg. It will be noted in this figure that 

 the cells are crowding together anterior to the polar organ. 



Development from figures i to 6 (PI. LIX) progresses very rapidly, so 

 much of the revolution being accomplished in a few hours. To obtain 

 these stages it was necessary to fix and examine large numbers of eggs 

 every few hours. 



Figures i to 3, Plate LX, show more advanced stages of the revolution 

 of the embryo and are especially interesting from the fact that they 

 illustrate the fate of the polar organ. It is very apparent that it merges 

 with and loses its identity in the large mass of cells that accumulate in 

 the cephalic region after the revolution of the embryo, which later forms 

 the dorsal organ. 



Figures 4 to 6, Plate LX, represent the fate of the dorsal organ after 

 its previous fusion with the polar organ. Under favorable weather 

 conditions the insect will hatch very soon after this point in the develop- 

 ment has been reached. 



1 Plate VII, figure i, of U. S. Dept. Agr. Bur. Ent. Bui. no is probably a little misleading, in that it 

 •would appear as though the serosa and amnion came in contact in the region of the ventral part of the 

 bead, which is not true. 



