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The Origin of the Sex-Cells of Chrysemys. 
By Bennet M. Aıtkn, 
Instructor in Anatomy, University of Wisconsin. 
With 15 Figures. 
Every one who has carefully studied the early stages in the em- 
bryonic development of the sex-glands of the Vertebrates, has at once 
had his attention attracted by certain large cells with sharply defined 
boundaries, clear cytoplasm, and large, rounded nucleus. In the early 
stages of those forms that develop from yolk-laden eggs, these cells 
are characterized by the presence in their cytoplasm of more or less 
numerous yolk granules which persist long after they have disappeared 
from the other cells of the embryo. These have been variously called 
sex-cells, germ-cells, primitive sex-cells, primordial ova, etc. We shall 
refer to them as sex-cells, after NusspAum’s Geschlechtszellen. This 
term will be used to include the progenitors of the odgonia and 
spermatogonia during those stages prior to the period when sex dif- 
ferentiation is clearly evident. 
The most important studies upon the origin of the sex-cells in the 
Vertebrates, have been made upon different groups of Fishes. Nuss- 
BAUM 780, MAcLxon ’81, Horrmann ’87, JUNGERSEN ’89, EIGENMANN ’92 
and ’96, and Boni ’04 worked upon different forms of Teleosts, while 
SEMPER 75, BaLrour ’78, Baupıanı ’79, RaBL ’96, Rtcxertr ’88, BEARD 
700 and ’04, and Woops ’02 studied this subject among the Elasmo- 
branchs. In this connection, mention should assuredly be made of 
WHEerer'’s (99) instructive work upon Petromyzon. Space will not 
permit a review of this literature; the reader may be referred to the 
recent paper by Bönı 704. 
The origin of the sex-cells has been studied in numerous forms of 
Batrachians and in quite early stages. To Goxrtre ’75, belongs the 
honor of having first recognized them in Bombinator. NussBaum ’80, 
first gave a true interpretation of their origin and fate. Mention should 
also be made of the work of Horrmann ’87 and of Bouin ’00. The last 
named author gives a review of the literature upon this subject. 
Braun 77, Miuarkovıcs ’85, and Horrmann ’89 have studied them 
in the early development of different forms of Reptiles, while Horr- 
MANN ’92, LauLanıe ’86, Janosik ’85 and ’90, Summon ’87, and Nuss- 
