33 W. M. WHEELER, The development of the urinogenital organs of the lamprey. 



Fig. 67. Stage 20. (Ammocœtes , 9,5 cm long.) Cross-section 

 through the developed portion of the left mesonephros and through 

 the reproductive organ (gon). The corpus adiposum is partially filled 

 with mesonephric tubules and blood vessels, but the dorsal portion of 

 the lobe is as yet scarcely invaded. The glomerulus on the inner side 

 and the pronephric duct in the edge the lobe have their definitive 

 position. 



Fig. 68, Stage 21. (Ammocœtes, 17 cm long.) Cross-section of 

 part of the pronephric duct and part of the left mesonephric lobe just 

 dorsal to it, about 21/3 cm in front of the anus. A young mesonephric 

 tubule is seen starting from the peritoneum and forcing its way through 

 the glandular wall of the duct. 



