JO SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 98 



Fig. 9. Enlargement of a portion of the section shown in figure 7 demonstrating 

 the division of the periplasm into cell territories. X 450. 



Fig. 10. Enlargement of a portion of the section shown in figure 3. Four 

 nuclei may be seen in the periplasm. X 450. 



Fig. 11. Similar to figure 10. X 450. 



Fig. 12. Longitudinal section through the anterior half of a Ctenocephalides 

 fclis egg in a stage just prior to syngamy showing one polar body 

 (PB) lying in the periplasm and the sperm (SN) and egg (EN) 

 nuclei among the vitelline spheres. Only one more nucleus, the other 

 polar body, showed in sections made from this egg. X 400. 



Fig. 13. Portion of a section through a Nosopsyllus fasciatns egg before 

 cleavage showing the effect of Heidenhain's iron haematoxylin on 

 the vitelline spheres. Some of the strands of the protoplasmic 

 reticulum may be seen between these black spheres. X 400. 



Plate 2 



Fig. 14. Sagittal section through an egg of Ctenocephalides felis showing the 

 early formations of the mesenteron rudiments. The flattening of the 

 germ band at the posterior pole, the first step in the formation of the 

 posterior mesenteron rudiment, is clearly demonstrated. The begin- 

 ning of the anterior mesenteron rudiment may be seen as a slight 

 thickening of the germ band just ventral to the anterior pole. 

 An enlargement of the posterior portion of this section is shown in 

 figure 51. X 100. 



Fig. 15. Portion of the anterior margin of a Ctenocephalides felis egg showing 

 the anterior mesenteron rudiment at a stage slightly later than that 

 shown in figure 16. As yet there is no indication of the amnio- 

 serosal fold. X 450. 



Fig. 16. Portion of the anterior margin of a Ctenocephalides felis egg showing 

 the anterior mesenteron rudiment at the beginning of its formation. 

 This stage corresponds to that shown in figure 14. X 450. 



Fig. 17. Transverse section through the anterior third of the germ band of a 

 Ctenocephalides fclis egg at a stage somewhat later than that shown 

 in figure 61, showing formation of the mesoderm by simple emigra- 

 tion of cells from the blastoderm. The embryonic membranes have 

 completed their formation above the germ band at this stage. 

 X400. 



Fig. 18. Horizontal section through a Ctenocephalides felis egg cutting the germ 

 band through the procephalic lobes at the anterior end and through 

 the region of mesodermal formation by the differentiation of a 

 distinct tube at the posterior pole. The amniotic cavity is apparent 

 above the tube. X 100. 



Fig. 19. Enlargement of the posterior portion of the section shown in figure 18. 

 This section is similar to that which is shown in figure 65. X 400. 



Fig. 20. Horizontal section through a Ctenocephalides felis egg at a stage 

 similar to that shown in figure 18 but at a somewhat more dorsal 

 level. The procephalic lobes show to better advantage in this 

 section. The plane of the cut follows the amnio-proctodaeal cavity 

 for a short distance where the tail of the embryo turns into the 

 vitellus at the posterior pole of the egg. X 100. 



