EXPERIMENTS WITH CHRYSOMELID BEETLES. 



243 



between this preparation and that of a normal embryo is the 

 absence of the primordial germ cells at the posterior end (see 

 Fig. 2, pgc). Three perfect series of sections were cut from eggs 

 at this stage, but none disclosed any germ cells. 



Fig. 9 is a sketch of embryo L.D. 018 63 (see Table II.). It 

 was killed two and one half days after the operation and is a 

 stage a trifle younger than that shown in Fig. 5. The tail fold 

 (//), however, is not fully developed as in Fig. 5. Longitudinal 

 sections were cut through two embryos like that shown in Fig. 9, 

 but no germ cells could be found. Fig. 10 was drawn from a 

 section through the tail fold of a normal embryo two and one 

 half days old ; it indicates where the germ cells (gc) are situated 

 at this time. If germ cells had been present in the embryo shown 

 in Fig. 9, they would certainly have been found. 



These experiments demonstrate that germ cells are not produced 

 when the extreme posterior end of the egg is prevented from 

 taking part in development, and it seems probable from the 

 method of origin of the germ cells that the destruction of the 

 germ cell determinants is the real cause of their absence. 1 



3. KILLING THE PRIMORDIAL GERM CELLS. 

 Table III. gives the data for the experiments performed in 

 series L.D. oil. Sixty-nine eggs were laid at n A.M. June 24, 



TABLE III. 



EXPERIMENTS IN KILLING THE PRIMORDIAL GERM CELLS. 

 Leptinotarsa decemlineala Series L.D. on. 



: The writer's papers on "The Origin and Early History of the Germ Cells in 

 some Chrysomelid Beetles" (Journ. Morph., Vol. 20) and on "Germ Cell Deter- 

 minants and Their Significance" now in press (American Naturalist) discuss these 

 points fully. 



