NO. 3 EMBRYOLOGY OF FLEAS KESSEL 9 



homologous to the sculpturings on the egg surfaces of other insects, 

 representing the imprints of the cells of the follicular epithelium. 



In section the chorion of the cat flea egg appears as an extremely 

 thin single membrane (pi. 4, figs. 39 to 42). By contrast, the chorions 

 of Nosopsyllus fasciatus and Hystrichopsylla dippiei are considerably 

 thicker. In the latter of these species this membrane appears as a 

 rigid shell made up of two laminae which are united by countless, 

 extremely slender, transversely arranged, supporting pillars (pi. 1. 

 fig. 2). These two chorionic layers appear to correspond to the 

 exochorion and endochorion which Blochmann (1887b) and Wheeler 

 (1889) have described for certain other insects. 



In all of the three flea species studied, a second protective covering- 

 lies beneath the chorion. This is the yolk or vitelline membrane 

 (pi. 6, fig. 53 ; pi. 11, fig. 79). It is thin in all species and, like the 

 chorion, is noncellular. Its relative position in regard to the chorion 

 and the yolk surface varies in different preparations, but as a rule it 

 lies nearer to the latter in the younger stages. The vitelline membrane 

 appears to be merely the attenuated limiting membrane of the develop- 

 ing oocyte which has been secreted by the superficial protoplasm. It 

 remains intact until the time of eclosion. 



Spermatozoa traverse the chorion and the vitelline membrane of 

 insect eggs by means of micropylar openings. In flea ova these are 

 arranged in two circular areas, one at each pole (pi. 1, fig. 1). These 

 micropylar apparatuses have been observed previously in the eggs of 

 Ctenocephalides jells by Balbiani (1875). The number of openings 

 at the respective poles in the eggs of any one species is variable, but 

 is always considerably greater at the anterior pole in any individual 

 egg. Furthermore, the minimum for the anterior pole number is 

 always somewhat greater than the maximum for the posterior pole 

 number in the same species. Balbiani found that in the case of cat 

 flea eggs the number of anterior micropylar openings varied from 

 45 to 50, whereas his counts gave only 25 to 30 such pores for the 

 posterior pole. However, the writer's counts show a greater variation 

 in the case of each pole. The micropylar openings at the anterior 

 pole were found to number as few as 35 or as many as 55, whereas 

 the posterior apparatus was found to consist of from 20 to 30 such 

 openings. 



It appears that the micropylar apparatuses in the eggs of Nosopsyl- 

 lus fasciatus and Hystrichopsylla dippiei have not been described 

 previously. In the former the number of openings at the respective 

 poles corresponds closely to the range given above for Ctenocephalides 

 fells. In Hystrichopsylla dippiei the pores are fewer in number at both 



