74 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 98 



Plate 7 



Fig. 55. Whole mount of a Ctenoccphalidcs felts embryo dissected from the 

 egg early in the third day of development. The germ band is unseg- 

 mented and the tail region is not entirely withdrawn from the 

 vitellus. At this stage the embryo consists of two general regions, 

 an anterior one widened to form the procephalic lobes and a 

 posterior unwidened one forming the protocormic region. X 115. 



Fig. 56. Sagittal section through a Ctenocephalides fclis egg at a stage slightly 

 younger than the one shown in figure 55 and corresponding to the 

 stage shown in figure 54. The posterior amnio-serosal fold grows 

 more rapidly than its anterior counterpart and may here be seen 

 approaching the midventral region of the egg. This stage illustrates 

 the maximum involution of the caudal region with the amnio- 

 proctodaeal cavity lying at the center of the vitellus. It also shows 

 how the germ band is carried around the inner extremity of this 

 lumen. X US- 



Fin. 57. Horizontal section through a Ctenocephalides felis egg in the same 

 stage of development as that shown in figure 55. The germ band is 

 cut transversely in three places, at the anterior end through the 

 procephalic lobes, at the middle of the egg through the tail where 

 the embryonic rudiment rounds the amnio-proctodaeal cavity, and 

 at the posterior end of the egg where the tail piece was originally 

 invaginated into the vitellus. The amniotic and serosal membranes 

 are complete and show at both poles of the egg. X 115. 



Fig. 58. Section through a Ctenocephalides felis egg showing the involuted 

 posterior portion of the germ band in transverse section at a plane 

 posterior to the posterior mesenteron rudiment and at the center 

 of the egg. The mesodermal cells may be seen migrating inward 

 from the blastoderm. The lumen shown is the inner extremity of 

 the amnio-proctodaeal cavity. X 400. 



Fig. 59. Sagittal section through the posterior region of the germ band of 

 Ctenocephalides felis at a stage similar to that shown in figures 56, 

 58, and 60. The posterior mesenteron rudiment cells are to be seen 

 lying below the ectoderm adjacent to the posterior terminus of the 

 amnio-proctodaeal cavity. X 400. 



Fig. 60. Parasagittal section similar to the sagittal one shown in figure 59. 

 X4C-0. 



Plate 8 



Fig. 61. Transverse section through the germ band of Ctenocephalides felis 

 at a point between the anterior amnio-serosal fold and the anterior 

 mesenteron rudiment showing mesoderm formation by simple 

 emigration of cells from the blastoderm. X 400. 



Fig. 62. Transverse section through the germ band of Ctenocephalides felis 

 at a point in the anterior portion of its second third in that region 

 of the embryonic rudiment where mesoderm formation is by the 

 migration of cells from the blastoderm together with the formation 

 of a groove. X 400. 



