IV 



PRONEPHROS 



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. 



puc. 



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, endoderm ; gl, glome- 

 rulus ; M, liver ; my, inyotome ; X, notochord ; nc, nephrocoele ; oes, oesophagus ; pn, pronephric 

 tubule; p.v.c, posterior vena cava ; >/>/<. sjilanchnocoele. 



ACTINOPTERYGII. 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. 



