DEVELOPMENT OF NEPHRIDIA OF PHERETIMA 



71 



Text-fig. 3. 



A series of three diagrams showing the common origin and develop- 

 ment of the three types of nephridia in P h e r e t i m a embryos. 

 In A (left half) the integumentary nephridia are seen pushing 

 themselves into the coelomic chambers while the ' funnel-cells ' 

 are travelling dorsalwards between the adjoining coelomic 

 chambers. The origin of the pharyngeal nephridia and ducts is 

 also shown. The right half shows the nephridia at a more advanced 

 stage of development. Septal nephridia are developing between 

 the adjoining peritoneal sheets, while the ducts of the pharyngeal 

 nephridia are formed even before the nephridia themselves are fully 

 formed. In B (on the left) is shown the development of secondary 

 nephridia, while the right half shows more or less the adult 

 condition of nephridia in the worm, n.t., nephridial teloblasts ; 

 nph.c, cells of the nephridial row ; c.c, coelomic cavities ; 

 int.nph., integumentary nephridia ; s.w., septal nephridia ; 

 s.n.r., rudiment of a septal nephridia ; fh.wph., pharyngeal 

 nephridium ; ph.d., duct of pharyngeal nephridia ; (j., gut ; 

 s.i.d., supra-intestinal excretory duct ; f.c, funnel-cells. 



