27* SCIENCE PROGRESS 



the complete amount of chromatin, is also determined by the 

 cytoplasm. 



Because of the fact that it is hermaphroditic, the early history 

 of the germ cells in the arrow worm, Sagitta, is of peculiar 

 interest. In the mature egg of this animal, Elpatiewsky (17) 

 discovered a peculiar body (the " besondcre Korper") which 

 becomes segregated in one cell (the stem cell) until the thirty- 

 two-cell stage. The cell containing it may then be identified as 

 the primordial germ cell. When this cell divides, the " beson- 

 dere Korper" is apparently unequally distributed between the 

 two daughter cells, one of which is considered an oogonium, 

 the other a spermatogonium. Stevens (18) and Buchner(io) 

 have confirmed Elpatiewsky's results, but whether or not the 

 division of the primordial germ cell is differential has not yet 

 been definitely determined. 



Many recent reports have been published upon the germ 

 cells of vertebrates, and for a time it seemed from the researches 

 of Rubaschkin (20) and Tschaschkin (21) that the new methods 

 devised for the purpose of staining the mitochondria might aid 

 us in solving the problem of the origin of the germ cells in this 

 group ; but later investigators, such as von Berenberg-Gossler 

 (22) and Swift (23), have been unable to discover any distinction 

 between the mitochondria in the germ cells and those in the 

 somatic cells of vertebrate embryos. Dodds (24) has found in 

 the teleost, Lophius, an inclusion in the cytoplasm of the germ 

 cells in young embryos which he thinks may be of nucleolar 

 origin, and Swift has recorded an especially large attraction 

 sphere in the earliest recognisable germ cells of chick embryos, 

 so there is still ground for the hope that some method may 

 yet be found for tracing these cells to their true origin in the 

 vertebrates. 



In the cases cited above, the stem cell, the primordial germ 

 cell or cells, and the early oogonia and spermatogonia are visibly 

 different from the other cells of the embryo because of the pre- 

 sence of inclusions in their cytoplasm. In only a few species 

 do we know the genesis of these keimbahn-determinants. In 

 the parasitic hymenopteron, Copidosoma, they consist of all of 

 the chromatin from an oocyte nucleus. In chrysomelid beetles 

 they may consist of chromatin, or may be derived from the food 

 stream. Haecker and Amma consider the ectosomes of the 

 copepods to be by-products of metabolism, and Kuhn has shown 



