312 



Orioin and Mis-ration of the Germ-Cells in Acantliias 



Dnring these early stages from 9 njD to 30 soinites more or less, the 

 primitive ova always lie at the hind end of the embryo where the germ 

 layers meet or are also a little anterior to this jnnction. In the yonngest 

 embryo before the medullary groove has closed, they lie quite far out- 

 on the sides and always in the blastodermic rim. 



Fig. 4 is from a 3 mm. embryo. The germ-cells are found near the 

 junction of the three germ layers and are nearer the median Hue than 

 in Fiff. 3. 



Fig. 4. Embr}'0 3 mm. Eu. eudoderm, germ-cells as black dots. x 38. 

 Fig. .5. Embryo o^o mm. Eu. eudoderm, Ur. g-erm-cells. Harvard Embryological 

 Collection. Traus. Series 463, section 14T. x 38. 



The next section, Fig. 5, is from an embryo of 3i mm. This shows 

 the primitive ova at the junction of the mesoderm and eudoderm, hud- 

 dled together in a characteristic tumor-like ball as they lie before their 

 journey upwards into the segmented mesoderm and genital region. 



Fig. 6. Section of germ-cell region drawn with oil-immersion objective. Embryo 

 of 3}4 mm. Ec. ectoderm, En. endoderm, Mes. mesoderm, Ur. germ-cells. x 330. 



This cluster is where most of the primitive ova lie and is just anterior 

 to the last body segment where the three germ layers come in contact. 

 A little mass like this is found on both sides of the body in all embryos 

 between about 3 and 4 mm., and is so conspicuous as to be easily seen 



