112 



ZOOLOGY 



SECT. 



(B, ms. nph.) from which the permanent kidney is formed in most 

 of the lower Craniata. The mesonephric nephridia open at one 



CLTL 



Fic. 747. Diagrams illustrating the development of the urinogeuital organs of Craniata. 

 A, development of proiiephros and segmental duct ; B, atrophy of pronephros, development 

 of mesonephros ; C, differentiation of pro- and meso-nephric ducts ; D, development of meta- 

 nephros, male type; E, female type. al. bl. allantoric bladder; an. anus; cl. cloaca; gon. 

 gonad ; int. intestine; //i.e. Malpighian capsule; ms.n.tl. mesonephric duct; //<*. ////A. 

 mesonephros ; mt. n. '. metanephric duct ; mt. nph. metanephros ; nst. nephrostomc ; or 

 ovary ; j). n. d. pronephric duct ; p. nph. pronephros ; sg. (?. segmental duct ; t. testis ; <. (. 

 vasa efferentia. 



end into the segmental duct (sg, rf.), at the other, by ciliated 

 funnels (nst.), into the ccelome ; a short distance from the funnel 



