EXPERIMENTS WITH CHRYSOMELID BEETLES. 25! 



ments former experiments in removing the germ cell determi- 

 nants, and indicates that these granules really determine the germ 

 cells. 



2. When the primordial germ cells of Leptinotarsa decemlineata 

 are killed in the blastoderm stage (Fig. 2, pgc) the resulting 

 embryos lack germ cells. This is the earliest known stage in 

 which surgical castration has been performed among the Insecta. 



3. When the anterior or posterior parts of freshly laid eggs 

 (Fig. i) are killed, the material remaining alive develops that 

 part of the embryo which it would have produced if the eggs 

 had remained intact (Fig. 1 1) . No regeneration of the part which 

 would have been produced by the killed region takes place. 



4. If the anterior or posterior parts of eggs in the blastoderm 

 stage (Fig. 2) are killed, the resulting tissue represents the parts 

 of the embryos which would have been produced by the living 

 material if the entire egg had been allowed to develop (Figs. 8 

 and 9). 



5. When parts of young embryos (Fig. 4) are killed, the re- 

 maining tissue develops normally (Figs. 15-18). Even small 

 pieces of tissue (Fig. 17, //), which are widely separated from the 

 rest of the embryo, continue to develop normally. 



6. Parts of old embryos develop up to the time of hatching. 

 There is no regeneration of the killed part by the living tissue, 



7. The eggs of Leptinotarsa decemlineata, at the time of depo- 

 sition (Fig. i), are definitely oriented with respect to the future 

 position of the embryo. 1 The areas of the peripheral layer of 

 cytoplasm (Fig. I, khbl) are already set aside for the production 

 of particular parts of the embryo, and if these areas are killed, 

 the parts of the embryo to which they were destined to give rise 

 will not appear. Likewise areas of the blastoderm (Fig. 2, bl) 

 are destined to produce certain particular parts of the embryo. 



THE UNIVERSITY OF MICHIGAN, 

 February 6, 1911. 



1 Hegner, R. W., '09, "The Effects of Centrifugal Force upon the Eggs of Some 

 Chrysomelid Beetles." Journ. Exp. Zoo/. Vol. 6. 



