NO. 3 EMBRYOLOGY OF FLEAS KESSEL 63 



cells which have separated into two groups and migrated laterally and 

 anteriorly during the development of the embryo. The gonads lie in 

 abdominal segments four to six. A mesodermal strand, the genital 

 duct anlage, passes posteriorly from the body of the gonad. 



Other mesodermal derivatives are the muscles, fat cells, haemato- 

 cytes, and the limiting walls of the circulatory system. From the 

 ectoderm are derived such additional structures as the tracheae and 

 tracheoles, the oenocytes, the endoskeleton, the labial and silk glands, 

 the corpora allata, parts of the genital tract, and the epidermis together 

 with its secondary structures such as the cuticle, the setae, and the 

 hatching spine. 



Hatching occurs after 6 days of development under the temperature 

 and relative humidity standards followed in this study. After swal- 

 lowing the amniotic fluid, the young larva escapes from the egg 

 through a slit in the shell made either by the hatching spine alone or 

 by this spine aided by muscular contractions of the body. 



LITERATURE CITED 



Auten, Mary 



1934. The early embryological development of Phormia regina: Diptera 



(Calliphoridae). Ann. Ent. Soc. Amer., vol. 27, pp. 481-499. 

 Ayers, H. 



1884. On the development of Oecanthus nivcus and its parasite Teleas. 



Mem. Boston Soc. Nat. Hist., vol. 3, pp. 225-281. 

 Baker, C. F. 



1905. The classification of the American Siphonaptera. Proc. U. S. Nat. 



Mus., vol. 29, pp. 121 -170. 

 Balbiani, E. G. 



1875. Sur l'embryogenie de la puce. C. R. Acad. Sci. Paris, vol. 81, 



pp. 901-906. 

 1882. Sur la signification des cellules polaires des insectes. C. R. Acad. 



Sci. Paris, vol. 95, pp. 927-929. 

 Blochmann, F. 



1884. Ueber eine Metamorphose der Kerne in den Ovarialeirn und iiber den 



Beginn der Blastodermbildung bei den Ameisen. Verhandl. Natur- 



hist.-Med. Ver. Heidelburg, pp. 243-247. 

 1886. Ueber die Reifung der Eier bei Ameisen und Wespen. Festschrift 



zur Feier des Funfhundertjahrigen Bestehens der Ruperto-Carola, 



dargebracht von dem Naturhist.-Med. Ver. Heidelburg, pp. 143-172. 

 1887a. Ueber das regelmassige Vorkommen von bacterienahlichen Gebilden 



in den Geweben und den Eiern verschiedener Insecten. Zeitschr. 



Biol., vol. 24, pp. 1-15. 

 1887b. Ueber die Richtungskorper bei Insekteneiern. Biol. Centbl., vol. 7, 



pp. 108-111. 



BOBRETZKY, N. 



1878. Ueber die Bildung der Blastoderms und der Keimblatter bei den 

 Insecten. Zeitschr. Wiss. Zool., vol. 31, pp. 195-215. 



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