8 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 98 



tend to become more opaque as they age, those of the cat flea are by 

 far the most transparent at every stage of development. Color dif- 

 ferences also become manifest as development progresses. The eggs 

 of the cat flea remain relatively colorless, those of the other two species 

 assume a cream color within a few hours after being laid. This colora- 

 tion is retained by the eggs of Hystrichopsylla dippiei, but in the case 

 of Nosopsylhis fasciatus the eggs often acquire a darker hue which 

 sometimes approaches a reddish brown before hatching. These varia- 

 tions in color and transparency are due primarily to chorionic differ- 

 ences between the species, correlated with differences in egg size. A 

 relatively thick chorion, combined with small egg size, makes an egg 

 m< ire opaque and darker in color. 



Of the three species here considered, the eggs of Hystrichopsylla 

 dippiei are much the largest, approximately 1.9 mm. in length and 

 0.9 mm. in greatest diameter. Corresponding measurements for the 

 two other species were 0.8 mm. and 0.4 mm. for Nosopsylhis fasciatus, 

 and 0.5 mm. and 0.3 mm. for Ctenocephalides felis. 



The outer surfaces of most insect eggs are sculptured with a reticu- 

 lum of slightly raised ridges which enclose polygonal spaces. These 

 markings represent the imprints of the ovarian follicle cells which 

 serve to secrete the chorion. In the eggs of Nosopsylhis fasciatus and 

 Hystrichopsylla dippiei this sculpturing of the chorion is rather pro- 

 nounced. However, in the cat flea egg it is scarcely perceptible, even 

 when the egg surface is thoroughly dried after oviposition. The 

 chorionic markings of this species are so indistinct that Balbiani 

 (1875) characterizes the chorion of the cat flea egg as unsculptured. 

 He says, "The rugose appearance, like scales, that the egg presents on 

 its surface, is not inherent in this membrane as Leuchart thought, but 

 is due to the coating that the egg receives at the moment of deposition." 

 Balbiani does not state what procedure he followed in reaching this 

 conclusion, but it may be assumed that he failed to see markings on 

 the chorionic surfaces of eggs dissected directly from the ovarioles. 

 A failure of this type is attributable to the fact that as long as the 

 chorion is wet its sculpturing is difficult to make out. This is true 

 even in the case of Nosopsyllus fasciatus or Hystrichopsylla dippiei 

 eggs in which the reticulations of the chorion are very evident when 

 this membrane is dry. As cat flea eggs tend to collapse in a short time 

 after they are dissected from the ovariole, it is probable that Balbiani 

 examined the eggs before they had dried sufficiently to show the 

 chorionic sculpturings clearly. The faint reticulations which may be 

 seen on the chorion of the Ctenocephalides felis egg are without doubt 



