450 ' ROBERT W, HEGNER 



semys, Rana, Amia and Lepidosteus, Rubaschkin ('07, '09, '10, 

 '12) in the chick, cat, rabbit and guinea-pig, Kuschakewitsch 

 ('08) in Rana, Jarvis ('08) in Phrynosoma, Tschaschin ('10) in 

 the chick, von Berenberg-Gossler ('12) in the chick, Schapitz 

 ('12) in Amblystoma, and Fuss ('12) in the pig and man. This 

 is by no nieans a complete list, but indicates the range of forms 

 studied and the current interest in this subject. No attempt 

 will be made here to review this mass of literature, but interesting 

 facts will be selected from several papers in the list. 



In the first place, the vertebrates do not furnish as favorable 

 material for germ cell studies as do many of the invertebrates, 

 and a large number of the contributions have not added any- 

 thing particularly important to our knowledge of the subject, but 

 have simply demonstrated that similar conditions prevail among 

 members of different classes, orders, etc. One author (Eigen- 

 mann, '91, '96) believes that the germ cells in Cymatogaster are 

 differentiated as such in the thirty-two cell stage. This, however, 

 was not proved and no confirmatory data have since been fur- 

 nished. Within the past three years, however, several communi- 

 cations have been published which give us hope of really tracing 

 the Keimbahn back into the cleavage stages. Before this time 

 some of the characteristics by means of which germ cells could 

 be distinguished in vertebrate embryos were as follows: (1) 

 the presence of yolk, (2) an amoeboid shape, (3) large size, and 

 (4) slight staining capacity. Of the more recent investigations, 

 I shall mention those carried on by Dodds ('10), Rubaschkin 

 ('10, '12), Tschaschin ('10), and von Berenberg-Gossler ('12). 



One fact discovered by Dodds ('10) in the teleost, Lophius, is 

 of special interest, namely that the germ cells in the embryos 

 of this fish cannot be definitely distinguished previous to the 

 appearance in their cytoplasm of a body which stains like a 

 plasmosome (fig. 23, C). Germ cells are undoubtedly segre- 

 gated before this period, but they exhibited no characteristics 

 with the methods employed which rendered them distinguish- 

 able. Dodds believes that this cytoplasmic body is extruded 

 plasmosome material, probably part of one of the two plasmosomes 

 possessed by many of the cells at this period. Thus far Lophius 



