84 



KIDNE YS 



Now such ;i complete tubule is rarely found in the pronephros 

 (Figs. 55, A; 56, A). It occurs, however, in Ganoids, Apoda (Grymno- 



OV. 



Fig. 55. 



Diagrams of the urinogenital organs of the Craniata, seen in transverse sections of the trunk. 

 A. pronephros; 15. mesonephros ; C, young stage in development of male; D, adult male; E, 

 female with ' free' ovary ; F, female with closed ovisac {Lepidosteus ami most Teleostei). a.cl, 

 archinephric duct (which becomes tin- mesonephric duct in all except A); ao, aorta ; ar, arterj 

 to glomerulus : <\ main tubule ; c.o, cavity of ovary closed oil'; c.w, wall of eoelom : g, genital 

 ridge; m, mesentery; m.ii, Mullerian duct; m.f, Mullerian fold (developing duct); ms.c, 

 mesonephric capsule; ms.d, mesonephric duct; msj, mesonephric funnel; nt, notochord ; os, 

 ostium of oviduct ; ov, ovary; pj. pronephric funnel ; v.c, cardinal vein. 



phiona), and less typically in Myxinoicls. As a rule, the pronephric 

 tubules gradually dwindle at the anterior and posterior end of the 

 ora;an, and even the middle tubules are often incomplete. For 



