Plate XVIII. 





a.jm.1-6, Anlagen of pronephric 

 tubules from the first to sixth. 

 a.sd., Anlage of segmental dnct. 

 ed., collecting duct, 

 eh., chorda dorsalis. 

 c.p., coelomic projection. 

 cut., cutis-layer of myotome. 

 fg., fore-gut. 

 ep., epiblast. 

 hy., hypoblast. 



J.m., lateral plate of mesoblast. 

 m.p., parietal layer of mesoblast. 



ms., mesoblast. 



')ni.T, II, &c., the first, second, &:c. 



myotome. 

 mvs., muscle-layer of myotome. 

 m.v., visceral layer of mesoblast. 



n., neural cord or canal. 



pp.c, pleuroperitoneal cavity. 



pt.1'6, prone[)hric tubules from the 

 first to sixth. 



.sc/^, subchorda. 



sd., segmental duct. 



Figs. 30-31. From the same series as figs. 20-29 of the last plate. 



Figs. 32-50. From a series of transverse sections through a younger embryo 



of Stage 11 r. 

 Fig-^. 51-58. From a series of transverse sections through an embryo of 



Stage HI. 

 Fig. 59. A section through an older embo3'o of Stage iir, the posterior 



continuation of which is shown in the next following plate (figs. 60-63). 



