76 GEORGO ORIHAY SHINJI 



the result of the study of the sectioned material, fixed and stained in 

 accordance with modern microscopic technique is the contribution 

 by Emeis ('15). The sole purpose of his article was to present 

 the history of the three ovarian elements, namely, the nurse cells, 

 the egg cell, and the epithelial cells. He did not, however, show 

 whether the epithelial cells, from which the egg and the nurse 

 cells develop, come from the primordial germ cells or from the 

 original mesoderm. He was also not sure w^hether or not a quan- 

 titative or qualitative cell division takes place among the early 

 oogonial and oocy tal cells. His cy tological accounts of the ovarian 

 cells do not include the phenomenon of the polar body formation. 

 Nevertheless, the most interesting feature of the article is the 

 discovery of the symbiotic organisms in the egg as well as in the 

 epithelial cells. 



As the foregoing brief survey of literature indicates, two phases 

 only of the development have been confirmed. The rest of the 

 accounts still remain to be confirmed or rejected, while the origin 

 and subsequent history of the pseudovitellus and the Pseudo- 

 navicellae demand a new and careful investigation. Again the 

 development of several organs (respiratory, circulatory, sensory, 

 and secretory) remains entirely undescribed. 



The purpose, then, of this work is to contribute as much as 

 possible toward the embryology of certain scale insects, with, 

 however, especial reference to the history of the pseudovitellus, 

 the germ cells, germ layers, alimentary canal, and nervous system. 



Before going further, I take this opportunity to acknowledge 

 my indebtedness to Professor Haseman, of the University of 

 Missouri, with whom the work was carried on. My hearty 

 thanks are due to Mr. Hollinger, who not only helped me in the 

 collection and identification of the material, but also gave valu- 

 able information, and, above all, daily encouragement; and to 

 Mr. Severance, of the library, through whose effort many valuable 

 journals in the librarj^ of Congress and of other institutions were 

 made available to me. Last, but not least, obligation is due to 

 Professor Woodworth, of the University of California, with whom 

 the study of the cottony cushion scale was originally begun. 



