IV 



PEONEPHEOS 



233 



becomes apparent. The fully functional pronephros has two tubules 

 on each side, corresponding to the segments above mentioned : it 

 may be presumed that these are the survivors of , a once greater 

 number, though there is no record of other rudiments having been 

 actually observed. 



Fig. 129a. — Development of the pronephros in Lepidosiren as shown in transverse 



sections. 



D, stage 30 ; E, stage 31+. A, dorsal aorta ; a.n.d, archinephric duct ; end, endoderra ; gl, glome- 

 rulus ; li, liver ; my, myotome ; N, notochord ; tic, nephrocoele ; oes, oesophagus ; pn, pronephric 

 tubule ; p.v.c, posterior vena cava ; splc, splanchnocoele. 



Actinopteeygii. — The acquirement of a thorough knowledge of 

 the development in the more primitive members of the group — the 

 ganoids — is an essential preliminary to the proper comprehension 

 of the development of the more highly evolved Teleosts but un- 

 fortunately our knowledge of renal development in the ganoids is 

 still far from complete. 



