Centrifugal Force upon Beetles'' Eggs 



529 



pole-cell canal and into the embryo and lie near the end of the tail- 

 fold. The gray cap has not entirely disappeared, but what I take 

 to be a remnant of it is situated at the dorsal anterior surface. 



C.B. 2, d. A normal larva hatched from this egg in the average 

 length of time required for eggs of this beetle when developed under 

 natural conditions. 



TABLE VII 



Calligrapha higshyana — Series C.B. 5 



Series C.B. 5— Table VII 



This series of experiments was performed in order to discover if 

 centrifugal force would have any appreciable effect on an egg in 

 which the blastoderm has already been formed, and if so whether 

 or not the egg would at this late stage continue to develop and 

 eventually produce a larva. 



C.B. 5, a. The eggs of C. bigsbyana at the age of twenty-one 

 hours have usually reached a stage in which a blastoderm of a 

 single layer of cells completely covers the central yolk mass. 

 Scattered about irregularly among the yolk-globules are numerous 

 vitellophags. At the posterior pole are a number of cells lying in 

 a closely packed group between the vitelline membrane and the 

 egg (Fig. 3, pgc); these are the primordial germ-cells (pole-cells) 

 which a few hours earlier migrated through that part of the pos- 

 terior end occupied by the pole-disc, taking the granules of which 

 this is composed along with them. 



C.B. 5, b. The application of centrifugal force for two hours 

 has very little effect upon an egg twenty-one hours old as seen in 



