116 GEORGO ORIHAY SHINJI 



Several cases of germ-cell segregation during an early cleavage 

 stage have been recorded in Diptera. As early as 1862, Robin 

 described what seemed to be the primordial germ glands of 

 Tipulides culiciformis. According to this investigator, four to 

 eight buds were seen at the posterior end of the egg. A similar 

 observation was made by Weismann a year later in the egg of 

 Chironomus. On account of their position Weismann called 

 them 'die Polzellen.' Both Robin ('62) and Weismann ('63) 

 failed to trace these cells up to the formation of definite organs. 

 Metznikow ('65, '66) and Leuckart ('65), however, found that the 

 'Polzellen' of Weismann migrate into the body cavity of the 

 embryo and become the sex cells in Simula, Chironomus, Culex, 

 and Miastor. In the following Diptera, studied by several 

 investigators since then, germ cells first become differentiated 

 before the completion of the blastoderm : 



Chironomus, Grimm ('70). 



Chironomus, Weismann ('82). 



Chironomus, Balbiani ("82-85). 



Chironomus, Jaworowski ('82). 



Musca, Kowalevsky ('86). 



Miastor, Kahle ('88). 



Miastor, Voeltzkow ('89). 



Calliphora, Lucilia, Graber ('89). 



Chironomus, Ritter ('90). 



Musca, Escherich ('00). 



Calliphora, Noack ('01). 



Chironomus, Hasper ('11). 



Miastor, Hegner ('13-14). 



Meyer ('49) could not find the genital organs of Liparia auriflua, 

 one of the Lepidoptera, until the caterpillars were over three 

 weeks old, while Balnini ('69-72) found them in the embryo of 

 Tinea crinella at about the time the segmented appendages make 

 their appearance. 



Woodworth ('89) and Schwangart ('05), however, found a 

 comparatively early differentiation of germ cells in certain butter- 

 flies. They found a thickening of the blastoderm near the 

 posterior end of the egg, the inner cells of which differentiate 



