2 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 98 



of cat flea eggs and observed that in them the chorion is more trans- 

 parent than in the ova of other siphonapteran species. He recognized 

 the inadequacy of the study of whole eggs, for he says in this paper, 

 "The delicate question of embryology can only be studied with profit 

 by the sectioning method, but the egg of the flea is too small to bear 

 this mode of investigation." Balbiani can scarcely be blamed for 

 reaching this conclusion when the small size of cat flea eggs is con- 

 sidered together with the fact that at that time no insect eggs had been 

 sectioned with any degree of success. Considering the absence of 

 efficient microtomes and biological stains, necessitating the limited 

 methods of research employed by Balbiani and his two predecessors in 

 the investigation of flea embryology, the results which these pioneers 

 obtained must be admired. Although obviously superficial, as well as 

 inaccurate in some instances, the papers of these first students of 

 flea development are, nevertheless, definitely superior to those of the 

 two writers on this subject who followed them and who had many of 

 the technical advantages of modern equipment. 



The first One to utilize the section method in studying flea eggs was 

 Tikhomirowa (1890). This paper is not available to the writer, but 

 a review of the main points given therein is presented by its author 

 in another of her papers (1892) which deals with the development of 

 Chrysopa, For the most part her conclusions regarding flea develop- 

 ment are inaccurate. 



Strindberg (1917) was the second to apply the section method to 

 the investigation of pulicine embryology. His brief paper is concerned 

 only with the intermediate developmental phases of Archeopsylla 

 erinacei (Bouche). Concerning the other periods he says: "The 

 early embryonic stages scarcely present worthwhile observations." 

 "The later embryonic stages do not show anything worthy of note 

 and therefore are not taken into account." A critical examination of 

 this author's statements necessitates the conclusion that his material 

 was very inadequate. 



The second respect in which the study of flea embryology is of 

 particular interest is that which is concerned with its application to the 

 phylogenetic position of the Siphonaptera. A study of the literature 

 suggests that there has been more speculation on the subject of the 

 affinities of the fleas than of any other insect order. This interest in 

 the natural relationships of fleas seems to have been the chief stimulus 

 which has prompted previous investigators to undertake studies of 

 their development, for their papers include discussions of the racial 

 origin of these insects. While accurate comparative embryological 

 observations are invaluable in the solution of phylogenetic problems, 



