22 R. W. HEGNER. 



when laid. They were carefully placed with the posterior end 

 up in small cavities in a block of paraffine. With the aid of a 

 binocular microscope the point of a fine needle was then inserted 

 at the center of this end, thus allowing that portion of the egg 

 containing the pole-disc granules or primordial germ-cells to flow 

 out. After removing this the eggs were placed in watch glasses 

 and allowed to develop to the desired stage. Some difficulty 

 was experienced in removing the proper amount of material and 

 a number of the eggs either developed into shapeless masses of 

 tissue or did not fix properly. These sources of error are in large 

 part responsible for the failure to obtain more definite results. 



I. THE EFFECTS OF REMOVING THE POLE-DISC GRANULES. 



1. C. niultipnnctata, Exp. C.m. i. One egg of C. unilti- 

 pnnctata was laid on April 15, 1908, and operated on while 

 fresh. The portion removed from the posterior end was fixed 

 on a slide and stained. It was found to contain the pole-disc 

 granules. This egg did not hatch in the average period (5 ^ 

 days) and so was preserved at the age of 8 days. 1 The embryo 

 appeared to be normal in every way, but on sectioning it was 

 found to be lacking not only in germ-cells but also in other ab- 

 dominal tissues. The mid- and hind-intestines were not com- 

 pletely formed and other neighboring parts were likewise de- 

 ficient. It is evident that the germ-cell determinants were re- 

 moved by the operation and that so much of the other organ- 

 forming substances was also removed that the embryo failed to 

 develop the corresponding tissues. 



2. C. liuiata, Exp. C. I. An egg of C. lunata which was laid 

 at 12 o'clock noon July 16, was operated at 2 p. m. on the same 

 day and fixed forty-nine hours later. It was stained in toto with 

 haemalum, drawn and then sectioned. Externally it resembled 

 exactly embryos of this age developed from entire eggs. Germ- 

 cells were found in the last two abdominal segments in a position 

 similar to that occupied by them in normal embryos. However, 

 there were not sixty-four, as was found to be the case in 

 embryos of C. mnltipitnctata, but only thirty germ-cells could be 



1 It has often been observed that when eggs of this beetle do not hatch the em- 

 bryos live for several days after the expiration of the regular hatching period. 



