290 The Alligator and Its Allies 



actual nephrostomes are to be seen, though the 

 occasional fusion of a tubule with the peritoneal 

 epithelium, as is seen on the left side of the present 

 figure, may represent such an opening. 



Figure 13^ is about one hundred and forty sec- 

 tions posterior to the section just described. The 

 embryo is here very slender, so that the contrast 

 between this and the first figure (13a) of this stage 

 is remarkable. Except in size, this section does 

 not differ greatly from the preceding. The spinal 

 cord, notochord, etc., are smaller than before, 

 but are of about the same relative size. The 

 mesentery {ms) in the section drawn was torn 

 across, so that the intestine is not represented. 

 Medial to the Wolffian duct is a tubule {wt), 

 which seems to be the same as those which were 

 called Wolffian tubules in the preceding stage, 

 but which may be the beginning of the ureter. 



Figure 13/, about two hundred and fifty sections 

 posterior to the last, passes through the extreme 

 posterior end of the embryo. The section is 

 nearly circular in outline and is somewhat larger 

 than the preceding. The amnion {a) completely 

 encircles the embryo. The ectoderm {ec) is of 

 fairly even thickness, and the mesoblast which it 

 encloses is of the usual character. The spinal 

 cord {sc) is nearly circular in outline, as is its central 

 canal. The digestive tract {e7it) is larger in section 

 than it was in more anterior regions; it is nearly 

 circular in cross-section and its walls are made up of 



