ZOOLOGY: H. E. JORDAN 
275 
in complete harmony with the idea of a single uninterrupted line of 
sex cells from primordial germ cells to oogonia and spermagonia, and 
with the hypothesis of a vertebrate 'Keimbahn' or continuous ger- 
minal path. 
11. The variations in the distribution of the primordial germ cells 
during earlier embryonic stages described by various investigators 
for a number of vertebrate forms — as pertains both to their presence in 
blood vessels (chick, Swift; duck, von Berenberg-Gossler) and in various 
regions and tissues remote from the more direct and more usual ger- 
minal route (Wolffian duct and somatopleure in the lizard, von Berenberg- 
Gossler; and sympathetic ganglia in the loggerhead turtle, Jordan); 
and to their apparent primary (urodeles) or secondary (anurans and 
other vertebrates) derivation from the splanchnic layer of the lateral 
mesoderm — are incidental to their original location with respect to 
the embryonic area and the vascularizing mesoblast of the blastoderm, 
and to their ameboid capacity. Since the primordial germ cells are 
genetically directly related to neither of the secondary germ layers their 
origin in either (entoderm or mesoderm) has no fundamental significance. 
Since they are capable of ameboid activity, and may become included 
in blood vessels, they may migrate anywhere, and so occur in any lo- 
cation, from where they may subsequently migrate again to the more 
direct germinal path, or perhaps disintegrate. The fact of fundamental 
significance with respect to the primordial germ cells is their original 
extra-regional distribution and their direct genetic independence of 
the soma cells. 
A more complete paper, with illustrations, and a fuller review of the 
literature, will appear in a forthcoming volume from the Tortugas 
Laboratory of the Carnegie Institution of Washington. 
^ Waldeyer, W., Eierstock und Ei, Leipzig, 1870. 
2 Nussbaum, M., Arch. mikr. Anat., Bonn, 18, 1880. 
3 Gatenby, J. B., Q. J. Microsc. Sci., London, N. S., 61, 1916, (275-300). 
* Allen, B. M., Anat. Anz., Jena, 31, 1907, (339-347). 
6 King, H. D., /. Morph., Philadelphia, 19, 1908, (369-438). 
6 Felix, W., Keibel, and Mall, Human Embryology, Philadelphia, 2, 1912, (882-890). 
7Firket, J., Arch. Biol., Liege, 29, 1914, (478-521). 
sDustin, A. P., Ibid., 23, 1907, (411-522). 
9 Swift, C. H., Amer. J. Anat., Philadelphia, 15, 1914, (483-516). 
i« Swift, C. H., Ibid., 18, 1915, (441^70). 
" Swift, C. H., Ibid., 20, 1916, (375-410). 
12 Reagan, F. P., Anat. Rec, Philadelphia, 2, 1916, (251-268). 
13 von Berenberg-Gossler, H., Anat. Anz., Jena, 47, 1914, (241-263). 
14 Allen, B. M., /. Morph., Philadelphia, 22, 1911, (1-36). 
15 Allen, B. M., Anat. Anz., Jena, 29, 1906. 
16 Dustin, A. P., Arch. Biol, Liege, 25, 1910, (495-534). 
17 Woods, F. A., Amer. J. Anat., Baltimore, 1, 1902 (307-320). 
