DEVELOPMENT OF NEPHRIDIA OF PHERETIMA 103 



the development of secondary integumentary nephridia. sec.i.n., secondary 

 integumentary nephridia ; ep., epidermis ; circ.m., layer of circular 

 muscle-fibres ; long.m., layer of longitudinal muscles ; s.s., setal sacs. 

 x440. 



Fig. 18. — Longitudinal section of the anterior portion of an embryo 

 about 4-5 mm. in length reconstructed from serial sections, showing the 

 early development of pharyngeal nephridia and their ducts (both being 

 solid at this stage), ph^, phr,, ph^, pharyngeal nephridia of the fourth, 

 fifth, and sixth segments with their respective ducts ; phx., pharynx ; 

 i.g.^ integumentary nephridia of the seventh segment ; b.c, buccal cavity ; 

 e.g., cerebral ganglion ; ph.gl., pharyngeal gland-cell. 



Pig. 19. — Longitudinal section of the anterior portion of an embryo 

 about 6 mm. in length, showing the primary pharyngeal nephridia and the 

 buds of the secondary ones arising on the ducts, d.v., dorsal vessel ; 

 lat.oe.v., lateral oesophageal vessel. 



Fig. 20. — Three embryos of typical ages of Pheretima rodri- 

 c ens is, shown in natural size. A is an embryo about 4 mm. in length, 

 from sections of which figs. 5, 8, 9, and 22 are taken. B is an embryo 

 about 6 mm. in length, from sections of which figs. 17, 18, and 23 are 

 taken. Whole mounts shown in figs. 11, 12, 13, 14, and parts of 15 are 

 taken from embryos of about this age. C is an embryo about to hatch 

 out of the cocoon about 17 mm. in length. Figs. 16, 19, 20, and 21 are 

 taken from whole mounts or sections of embryos of this age. Nat. size. 



