74 GEORGO ORIHAY SHINJI 



fragmentary. One of the earliest works of this kind was by 

 Leydig ('54), who described and figured the general appearance 

 of the ovaries of Lecanium (Coccus) hesperidum and its eggs 

 with three nurse cells and an egg cell. Although he did not 

 actually describe the process of differentiation of the ovarian 

 elements, he claimed that nurse cells, egg cell, and the epithelial 

 cells must have arisen from undifferentiated germ glands. He 

 also described the formation of the embryo from the egg by 

 multipHcation of the single egg cell. The statement that this 

 form is really viviparous was made in this article. He also pointed 

 out the presence of numerous pseudonavicellae in this insect. 

 These organisms, according to him, migrate into the egg at 

 its posterior end and multiply rapidly by budding. 



Leuckart ('58) has also studied the ovarian structure of 

 Lecanium hesperidum and found that three nurse cells and 

 an egg cell developed from epithelial cells. Therefore he main- 

 tained, as his predecessor did, that the nurse cells and the egg 

 cell are the modifications of the epithelial cells. 



Lubbock ('59) also came to the same conclusion, namely, the 

 nurse cells, the egg cell, and the epithelial cells are all originally 

 undifferentiated cells of the germ rudiment. 



The most complete account of the development of coccids 

 was, however, presented by Mecznikow ('66). His work on 

 coccids is not so complete as was that for Aphids, Corixa, and 

 Cecidomia. Nevertheless, it covers the development of the 

 Aspidiotus nerii from a single egg-cell stage to the time of hatch- 

 ing. He described and figured a differentiated egg with its 

 germinal vesicle. The appearance of the 'Wulst' prior to the 

 formation of the blastoderm and the invagination of the blasto- 

 derm near the posterior pole of the egg were also mentioned. 

 One layer of the invaginated 'Keimhiigel' degenerated to form 

 the amnion while the other developed into the embryo proper. 

 However, he failed to observe the phenomenon of revolution of 

 the embryo. The entire alimentary canal, he thought might be 

 formed by further elongation of both stomodeum and proc- 

 todeum. He described and figured an early appearance of the 

 germ cells and of the pseudovitellus. 



