60 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 98 



by the hatching spine is longitudinal. If the larva happens to cut such 

 a slit along one entire side of the egg between the curvatures of the 

 poles, it is able to crawl out. If, however, the hatching spine slips out 

 of the cut and the slit in the chorion is too small to allow an escape, 

 muscular contractions of the larva's body may be used to tear the 

 shell open far enough to allow an escape. The hatching spine of fleas 

 is definitely a part of the first instar larval cuticula and is retained, 

 consequently, until the first ecdysis. 



SUMMARY 



Ctenocephalides felis (Bouche), Nosopsylhts fasciatus (Bosc), 

 and Hystrichopsylla dippiei Roths, are the species studied. Except 

 for variations in the external characteristics of the eggs, no specific 

 differences were observed. 



Satisfactory sections of the eggs at all stages of development were 

 obtained by the use of a double imbedding combination technique 

 involving modifications of Boycott's clove oil celloidin and Wall's hot 

 celloidin methods. Tertiary butyl alcohol was used for all dehydration 

 series. 



The eggs are centrolecithal. The periplasm of the egg is reached by 

 spermatozoa by means of micropylar openings which are arranged 

 in circular areas, one at each pole. 



Maturation of the female pronucleus occurs in the anterior peri- 

 plasm. Syngamy occurs in the central region of the egg, as a rule 

 somewhat toward the anterior pole. The periplasm is very thin except 

 at the posterior pole where it is widened to form the posterior polar- 

 plasmic cap. An inner protoplasmic reticulum is continuous with the 

 periplasmic layer and ramifies throughout the vitellus. 



Cleavage is meroblastic peripheral. The periplasm is first supplied 

 with nuclei following the seventh cleavage division. The nuclei usually 

 reach the periplasm at all points simultaneously. Four blastema sub- 

 stages are recognized. Blastulation consists of the delimitation of 

 the nucleated periplasm of the last blastema substage into cell terri- 

 tories. Three blastula substages are evident. The second blastula 

 substage is produced by a concentration of cells toward the ventral 

 surface. The third blastula substage follows the eleventh mitotic divi- 

 sion which involves only the cells of the thickened blastoderm, thus 

 producing the anlage of the ventral plate. Cell accumulations produced 

 by emigration from the blastoderm appear near the anterior and 

 posterior extremities of the ventral plate. These are the mesenteron 

 rudiments. 



