THE EARTHWORM 



mes. 



A. Lateral view of an embryo of Lutnbricus f(.vtidus^ in which the germ bands are 

 clearly visible. />'. Ventral view of the same embryo. C. Lateral view of an older 

 embryo. D. Transverse section through the ventral half of an embryo, showing 

 the cleavage of the mesoblast. E. Early stage in the development of a nephridium 

 of RhynchelmiS) showing the pronephridiostome with a single flagellum. /''. A 

 later stage in the development of a nephridium. G. Nephridium in the eleventh 

 somite of a young worm. //. View of an older embryo of Lumbricus. ec, ecto- 

 derm ; en, endoderm ; ent, enteron ; ext, external pore of nephridium ; go, 

 gonad ; fries, mesoderm ; ;;/;//, mesomeres ; nep, nephroblasts ; neur, neuro- 

 blasts ; ///, nephridia ; pnp, pronephrostome ; .?..$, septa ; st, stomodaeum. (A 

 to D after E. B. Wilson ; E to G after Vejdovsky ; H after Kowalevsky.) 



