272 
ZOOLOGY: H. E. JORDAN 
These two rival theories have had their adherents to the present 
day. Gatenby,^ for example, claims that in certain amphibia {Rana 
temporaria, Salamandra) the definitive germ cells arise by process of 
transformation of peritoneal cells, as first described by Waldeyer; in 
similar forms {Rana pipeins; Bufo lentiginosus) Allen"^ and King^ claim 
that the definitive germ cells (gonia) and the primordial germ cells are 
the same, the former being genetic derivatives of the latter, and that 
neither are genetically related to the peritoneal epithelium. 
A number of investigators, e.g., Felix,^ Firket^ and Dustin^ claim 
the existence of two generations of germ cells, the primary and sec- 
ondary genital (sex) cells or gonocytes. The earlier generation is sup- 
posed to have only a phylogenetic significance and to early disappear 
after a more or less nomadic career; while the later generation is claimed 
to have its origin from the cells of the peritoneum covering the gonads. 
As regards the chick, Nussbaum's original claim is now fully sus- 
tained both on the basis of morphologic and of experimental data. 
Swift^ has discovered the original entodermal locus of the primordial 
germ cells in this form in a cephalic crescentic area, in the early primi- 
tive-streak stage. As the spreading mesoderm invades this region 
the germ cells become largely involved in the blood vessels, by which 
they are carried to the splanchnic mesoderm of the hind-gut region; 
from whence, by ameboid activity, they wander up the forming mesen- 
tery and across the celomic angle into the developing gonads. An 
unbroken lineage has now been traced by Swift^*^' between these 
primordial germ cells of the gonads and the oogonia and spermogonia 
of the ovary and testis respectively, without any contribution from 
the peritoneal epithelium. Reagan^^ j^as put Swift's observations 
to a crucial experimental test by removing the crescentic germ-cell 
area of the primitive-streak stage, and reincubating such operated 
specimens. Sections of such chick embryos revealed a complete lack 
of germ cells. 
Subsidiary more important matters concern the migration route 
of the primordial germ cells, and the possibility of a persistence of 
latent 'stray' germ cells to serve as possible future foci for neoplasms. 
In the chick (Swift) and in the duck (von Berenberg-Gossler^O the 
germ cells are said to migrate largely via the blood vessels. These 
observations involve the possibility of a confusion with hypertrophied 
blood granulocytes. Moreover, von Berenberg-Gossler^^ records the 
anomolous observation that in the lizard, Lacerta agilis, 'primordial 
germ cells' ('entodermal wandering cells') contribute to the formation 
of the caudal extremity of the Wolffian duct. He regards these cells 
