EXPERIMENTS WITH CHRYSOMELID BEETLES. 247 



the tissue destined to produce the abdomen, but also that set 

 aside to form the thorax was killed by the operation. The region 

 of the blastoderm which normally develops into the head covers 

 a considerable area at the time the operation was performed. 

 This area lessens in extent when the germ band arises (Fig. 3, pi), 

 and, after the cephalic appendages appear (Fig, 4, a, m, m 1 , w 2 ), 

 the anterior end of the embryo shortens until the mouth parts 

 are closely crowded together (Figs. 5, 6 and 7). In egg L.D. 04 

 A3 (Fig. 13) the shortening of the embryo has resulted in the 

 uncovering of a large yolk area (y), and, though a comparatively 

 small part of the egg was killed (&), this portion bore the blas- 

 toderm which in normal eggs gives rise to the larger part of the 

 embryo, i. e., the thorax and abdomen. 



When the blastoderm surrounding the anterior end of the egg 

 is killed, only the posterior embryonic region develops from the 

 part which remains alive. This is shown in egg L.D. 04 63, 

 Fig. 14. Here the normal number of abdominal segments appear 

 as well as two thoracic segments (/),one of which has developed 

 a normal pair of legs. 



6. KILLING PARTS OF YOUNG EMBRYOS. 



The series of figures numbered 15 to 18 show what takes place 

 when parts of young embryos are killed and are thus prevented 

 from continuing development. Table V. gives the data of the 

 operations. The eggs, fifty-two in number, were laid at 10 A.M. 

 June 26; the operations were performed at 10 A.M. June 28, at 

 which time the eggs bore embryos similar to that shown in Fig. 4. 

 Four of the eggs were kept as controls; these hatched on July 2. 

 Approximately one half of the anterior end of twenty-four of 

 the eggs was killed with a hot needle; the posterior half of the 

 other twenty-four eggs was killed in like manner. In every 

 instance the part of the embryo which remained alive devel- 

 oped as though the egg had not been disturbed. 



Figs. 15 and 16 show two stages in the development of the 

 posterior part of the embryo, and Figs. 17 and 18 show corre- 

 sponding stages in the development of the anterior part of the 

 embryo. It is interesting to note that in the egg shown in Fig. 15 

 not only the anterior end of the embryo, but also the extreme 



