The germ-cells. 599 



Description of Plates. 



Plate 43 — 44. 



All the figures were drawn under the Zeiss-Abbe camera (No. 44a) 

 at the level of the stage of the microscope, length of tube 160 mm. The 

 magnification is 1500 diameters (Zeiss' 2 mm apochromatic n. ap. 1.30 

 with compens. ocular 12), except figs. 13, 26, 27, 51 and 52, in which 

 it is 750 (2 mm apochromatic, ocular 6). All the figures have been 

 reduced in the process of lithography to two-thirds of their original 

 sizes, and, therefore, the apparent magnifications are 1000 and 500 

 diameters. All the figures are from transverse sections of embryos or 

 from blastoderms of Raja hatis. 



The numbers refer to series/slide, row of sections, and section, 

 t signifies top of row, b bottom of row, that is to say, the counting of 

 the number of the section has been from the top of the row or its bot- 

 tom.^ Thus, 661/2, 8 r. 10 t. signifies: series 661, slide 2, row of 

 sections 8, 10th section from the top of the row. 



ep epiblast, g. c gut-cavity, g.n germinal nidus, hy gut or hypo- 

 blast, p pericardium, s.i.v subintestinal vein, so somatopleure, sp splan- 

 chnopleure. 



Plate 43. 



Fig. 1. Germ-cell in the normal position. 661/2, 8 r. 19 t. 9 mm 

 embryo. 



Fig. 2. A normally placed germ-cell. 622 /last r., 25 b. 9 mm. 



Fig. 3. A primary germ-cell from the germinal nidus of a 28 7^ mm 

 embryo, showing persistence of yolk and absence of same in the somatic 

 cells. 627/4, 5 r. 13 t. 



Fig. 4. A normally placed germ-cell of large size. 688/3, 2 r. 

 12 b. 9 mm. 



Fig. 5. A normally placed germ-cell. 687/2, 5 r. 2 t. 7 mm. 



Fig. 6. A primary germ-cell in the epiblast of the gill-region and 

 just beneath a gill -pouch. 3rd of 5 sections. 661/1, 4 r. 24 t. 

 9 mm. 



Zool. Jahrb. XVI. Abth. f. Morph. in 



