PLATE 1. 



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Fig. 3. 



Fig. 1.— Primary germ-cell of Pristiiiriis melnixostomus. The cytoplasm is glassy in 

 character and contains a large number of (blackened) yolk-plates. The nucleus 

 exhibits duplication, i.e., autonomy of paternal and maternal portions. 



Hio. 2.— Primary germ-cell of the skate. RaJLi b.itis. 



Fig. 3.— The conditions seen in two transverse sections (the 39th and 41st sections of a 

 row) of a 4i mm. embryo of Pristiurus. The lettering is as follows : sp. c. = 

 spinal cord, n. = notochord, my. = myotome, g. n. = germinal nidus, me. = meso- 

 .< a'' ^.P' ^ epiblast, hy. = hypoblast, y. s. = yolk-sac, g. c. = germ-cell. 



hiG. 4.--A dtanr,imm,itic section of an early skate-embryo. To illustrate the migrations 

 of the germ-cells along the germinal path, g. p., and showing germ-cells in various 

 abnormal situations. The lettering is as in Fig. 3, excepting so. m. = somatic 

 mesoblast, sp. m. =. splanchnic mesoblast. ao. = aorta. (After John Beard) 



