242 



ROBERT W. HEGNER. 



ordinary circumstances eggs sometimes become shapeless masses 

 of tissue or remain in the condition of the freshly laid egg, but 

 this fact does not explain the great number of cases observed 

 among the operated eggs. It is evident that many of the oper- 

 ated eggs failed to develop because of the conditions of the ex- 

 periments. For this reason only a few of the best defined em- 

 bryos have been selected for descriptive purposes. 



b| 



m 



ab 



ec 



9 



FIG. 8. Longitudinal secion through an egg of Leptinotarsa decemlineata 

 (L.D. 09 62). The posterior end was killed with a hot needle just after the egg 

 was laid (see Fig. i); the egg was then allowed to develop for twenty-four hours. 

 bl, blastoderm; gcd, germ cell determinants; k, portion of egg killed. 



FIG. 9. Side view of an egg of Leptinotarsa decemlineata (L.D. 018 63). The 

 posterior end was killed with a hot needle just after deposition (see Fig. i); the 

 egg was then allowed to develop for sixty hours, ab, abdomen; h, head; I, thoracic 

 appendages; tf, tail fold. 



FIG. 10. Longitudinal section through the tail fold of a normal embryo of 

 Leptinotarsa decemlineata sixty hours old, showing the germ cells (gc). ec, ecto- 

 derm; m, malpighian tubules. 



Fig. 8 is from a longitudinal section of an egg (L.D. 09 62) 

 which was operated upon just after deposition and was then 

 allowed to develop for twenty-four hours. This should be com- 

 pared with the normal egg at a similar stage of development 

 (Fig. 2). In the egg shown in Fig. 8 the germ cell determinants 

 (gcd) and a portion of the neighboring yolk and cytoplasm (k} 

 have been prevented from taking part in development. That 

 part of the egg which remained alive produced a blastoderm of 

 a single layer of cells (bl). The principal difference to be noted 



