Januaet 13, 1911] 



SCIENCE 



71 



y 



large range of amperages and frequencies be 

 made, but I am not certain that I shall be able 

 to carry these out in the near future. The 

 difficulties in the way of securing adequate 

 control of current when high amperages are 

 used are greater than may appear to the 

 casual reader. 



Knight Dunlap 

 Johns Hopkins Univeesitt, 

 December 20, 1910 



THE GERM CELL DETERMINANTS IN THE EGGS OF 

 CHRYSOMELID BEETLES 



Parts of my papers on " The Origin and 

 Early History of the Germ Cells in Some 

 Chrysomelid Beetles,"^ and " The Effects of 

 Removing the Germ Cell Determinants from 

 the Eggs of Some Chrysomelid Beetles "^ have 

 recently been subjected to criticism,' which, it 

 seems to me, needs some analysis. I have 

 shown in these papers that a disc-shaped mass 

 of darkly staining granules appears at the 

 posterior end of the eggs of certain chrysome- 

 lid beetles just before deposition. Because of 

 the shape of this mass and its position in the 

 egg, I have called it the " pole disc." During 

 the formation of the blastoderm, those cleav- 

 age products which, in their progress toward 

 the periphery, encounter the pole disc gran- 

 ules, gather these about themselves and con- 

 tinue their migration, finally becoming en- 

 tirely separated from the egg. They then lie 

 in a compact group at the posterior end. 

 These are the primordial germ cells ; they can 

 be traced back into the embryo, where they 

 separate into two groups which become the 

 germ glands. The conclusion was reached 

 that the cleavage products " are potentially 

 alike until in their migration toward the 

 periphery they reach the ' keimhautblastem.' 

 Then those which chance to encounter the 

 granules of the pole disc are differentiated by 

 their environment, i. e., the granules, into 

 germ cells ; all the other cleavage products be- 

 come somatic cells" (1908, p. 21). 



'J'oMm. Morph., Vol. 20, 1909, pp. 231-296. 

 'Biol. Bull., Vol. 16, 1908, pp. 19-26. 

 ^ Wieman, H. L., " The Pole Disc of Chrysom- 

 elid Eggs," Biol. Bull., Vol. 18, 1910, pp. 180-187. 



It was found to be possible to remove the 

 pole disc from freshly laid eggs by pricking 

 the posterior end with a needle and allowing 

 them to flow out. Eggs operated upon in this 

 way produced embryos and larvse either with- 

 out germ cells or with only a few. This experi- 

 mental evidence, added to that derived from 

 the morphological study, seemed to prove that 

 the pole disc granules were necessary for the 

 prodiiction of the primordial germ cells and, 

 in fact, determined them as such. This led 

 to the conclusion that the " granules of the 

 pole disc are therefore either the germ cell 

 determinants or the visible sign of the germ 

 cell determinants" (1908, p. 21). Eecent ex- 

 periments give additional evidence. When 

 the posterior ends of freshly laid eggs are 

 killed with a hot needle, thus preventing the 

 pole disc from taking part in development, 

 no germ cells are produced in the embryos 

 and larvse which develop from them. 



Wieman objects to the term " germ cell 

 determinant " since " the term implies the 

 attribute of certain potentialities that these 

 granules have not been shown to possess " 

 (1910, p. 180). He also objects to my hypoth- 

 esis that the pole disc granules consist of 

 chromatic material extruded by the nucleus of 

 the oogonium, and claims that " the granules 

 of the pole disc consist of particles derived 

 from the food stream of the ovum that form 

 an accumulation of the protoplasm in its pos- 

 terior part" (1910, p. 187). This is no doubt 

 correct. I did not attempt to discover the 

 origin of these granules, but concluded that 

 they were of nuclear material because of the 

 derivation of similar substances in the early 

 development of Ascaris, Cyclops and a num- 

 ber of insects. According to---WiBB3.^n, " the 

 granules are not all taken up by the cells 

 in their migration and the greater part 

 of them remains behind after the cells 

 have passed through" (p. 186). This is cer- 

 tainly not the case in the four species of 

 beetles that I have used in my work. 



Wieman suggests several possibilities as to 

 the ultimate origin and significance of the 

 pole disc granules. These possibilities were 



