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100 THE SPRING GRAIX-APHIS OK GREEN BUG. 



nitely segniented into niore or less spherical masses, separated by 

 thin walls, each area or mass containing a number of yolk granules 

 and from one to several cells. The polar organ is now almost spher- 

 ical, with a central, pear-shaped area of dense, structureless, non- 

 staining matter of a yellowish color, and an anterior opening. Al- 

 though this evidence is insufficient it possibly indicates that the func- 

 tion of this organ is excretory. The embryo reaches this stage of 

 development about the third day, under favorable conditions of 

 temperature. 



In Stage 7 (PL VI, tig. 1) the embryo has changed its position so 

 that from a side view it has the form of a reversed figure 6. The 

 portion that in the preceding stage was folded upon itself ventrally 

 has reversed its position and folded back dorsalry. The ovarian 

 yolk is now in the region of the first abdominal segments. It is in 

 contact with the embryo, and the group of cells that separated it 

 from the embryo in the preceding stage has assumed almost a spheri- 

 cal form, and a more posterior position, forming the genital organs 

 later on. 



The three primary regions, cephalic, thoracic, and abdominal, are 

 now sharply marked. Each region is distinctly segmented. The 

 cephalic region has 5 segments indicated, the thoracic 3, and the 

 abdominal 9, the last abdominal being relatively quite large. There 

 are now 15 conical appendages. The antenna? arise from the pos- 

 terior margin of each cephalic lobe . The labrum is between and slight- 

 ly anterior to the antennae. The mandibles are nearer the median 

 plane than the fundaments of the maxilla? and the labium. The next 

 three pairs of appendages represent the first, second, and third pairs 

 of legs. Plate V, figure 2, represents a surface view of stage 7, show- 

 ing the embryo straightened out and the position of the appendages. 

 All of these appendages are evaginations of the ectoderm, cross-sec- 

 tions showing an external layer of ectoderm cells and an inner layer 

 of mesoderm cells. 



The stomodseum (PI. VI, fig. 1) appears now as a simple invagina- 

 tion of the ectoderm, the posterior wall of the labrum forming its 

 ant erior wall. The proctodeum has not yet appeared, The salivary 

 glands (PL VI, fig. 1) are represented by a deep, bilobed, ectodermal 

 invagination between the cephalic and thoracic regions. There is 

 now a star-shaped mass of protoplasm about the nucleus of the 

 ovarian yolk cells and the yolk granules are grouped around these 

 cells. 



The primary } T olk is grouped very much as in the preceding stage 

 with the exception that the masses are smaller and do not contain as 

 many nuclei. 



The polar organ is smaller than formerly, with a smaller number 

 of cells. It still contains a yellowish mass and communicates with 

 the outer surface of the egg. 



