240 



ROBERT W. HEGNER. 



until the end of the tail-fold coincides with the posterior end of 

 the egg (Fig. 6). The larva (Fig. 7) usually appears in five or 

 six days. 1 



2. KILLING THE GERM CELL DETERMINANTS. 

 The method used in the experiments mentioned above to 

 remove the germ cell determinants was to prick the posterior 

 end of the freshly laid egg with a needle and allow them to flow 

 out. These experiments were not considered entirely successful, 

 since I was unable to determine in any case whether all of the 

 germ cell determinants had been removed. Some of the embryos 

 which developed from eggs operated upon in this way produced 



FIG. 5. Ventral view of an egg of Leptinotarsa decemlineata sixty hours after 

 deposition, ab, abdomen; h, head; t, thoracic appendages; tf, tail fold. 



FIG. 6. Ventral view of an egg of Leptinotarsa decemlineata seventy-two hours 

 after deposition, ab, abdomen; h, head; t, thoracic appendages. 



FIG. 7. Side view of a newly hatched larva of Leptinotarsa decemlineata. 



either a lesser number of germ cells than normal, or else no germ 

 cells at all. The conclusion was reached that if all of the germ 

 cell determinants are removed from the egg no germ cells will be 

 produced, and that the granules which constitute the pole disc 

 aj;e really germ cell determinants. 2 



Two series of experiments (L.D. 09 and L.D. 018) were carried 



iHegner, R. W., '080, "Observations on the Breeding Habits of Three Chry- 

 somelid Beetles, Calligrapha bigsbyana, C. multipunctata and C. lunata, Psyche 

 Vol. 15. 



2 For a discussion of this subject see Hegner, R. W., 'n, "The Germ Cell De- 

 terminants in the Eggs of Chrysomelid Beetles," Science, Vol. XXXIII., pp. 71-72. 



