NO. 3 EMBRYOLOGY OF FLEAS KESSEL JJ 



Plate ii 



Fig. 79. Dorsal portion of a transverse section through an embryo of Cteno- 

 cephalides felts at a stage just prior to dorsal closure showing the 

 absorption of the third dorsal organ by the vitellus. At the left a 

 layer of entodermal cells may be seen lining the yolk mass. To the 

 left of these is a portion of the definitive body cavity. Parts of the 

 chorionic and vitelline membranes are shown in the upper part of the 

 figure. This stage is similar to that shown in figure 24. X 400. 



Fig. 80. Sagittal section through a Ctenocephalides fclis embryo at a stage 

 somewhat more advanced than that shown in figure 75. The coiled 

 hind-intestine of this stage is shown cut through in several places 

 and the anterior mesenteron ribbons have formed a complete floor 

 of entoderm for the yolk mass. This entodermal lining is covered by 

 the splanchnic mesoderm and below this lies the haemocoel. A strip 

 of somatic mesoderm appears in the midventral region of the 

 embryo. X H5- 



Fig. 81. Sagittal section through the anterior region of a Ctenocephalides felis 

 embryo showing the inner end of the stomodaeum. The paired 

 anterior mesenteron rudiments have fused ventrally and their cells 

 are shown in this section lining the vitellus below the stomodaeum. 

 The fusion of these ribbons dorsal to the stomodaeum is just begin- 

 ning. X 400. 



Fig. 82. Sagittal section through the anterior portion of a Ctenocephalides felis 

 embryo showing the stomodaeal invagination and the labrum. X 400. 



Fig. 83. Horizontal section through the anterior region of a Ctenocephalides 

 fclis embryo showing the paired lateral mesenteron ribbons (MR) 

 lying adjacent to the yolk. X 400. 



Fig. 84. Portion of a section through a Ctenocephalides felis embryo showing 

 the hind-intestine cut at two places. Three of the developing 

 malpighian tubules may be seen communicating with the procto- 

 daeum in the lower one of the cuts shown here. X 400. 



Plate 12 



Fig. 85. Portion of a sagittal section through a Ctenocephalides felis embryo 

 showing several ganglia of the ventral nerve cord, each with its 

 two transverse neuropile tracts. X 400. 



Fig. 86. Transverse section through the head region of a Ctenocephalides fclis 

 embryo in a late stage of development. In the upper portion of this 

 figure, and on either side of the oesophagus, are to be seen the 

 paired posterior extremities of the supraoesophageal ganglion. The 

 suboesophageal ganglion lies below the oesophagus and in this 

 section is shown connected with the supraoesophageal ganglion by 

 the neuropile tracts of the circumocsophageal connectives. This 

 stage corresponds with that shown in figures 26 and 87. X 400. 



Fig. 87. Sagittal section through a Ctenocephalides felis embryo in the fifth 

 day of development shortly after ventral flexion. The proctodaeum 

 is a particularly conspicuous structure. The supraoesophageal 

 ganglion, the suboesophageal ganglion, and the chain of ventral 



