352 s. HATTA : 



Tliu>i, the tubules of the third, fourth, and fifth, pairs con- 

 tinue to grow, lühile the fird pair has disappeared^ in the early 

 part of the present stage (or at the end. of the foregoing stage) ; 

 the sixth has already coinmenced retrogression and the second, is 

 also growing iveaher and weaker. 



Tn the oldest embryo of this stage, there is to be seen no 

 marked change in tlie ])ronephros, but tlio peritoneal lining is 

 reduced into a very thin plate of :i deiinite epithelium every- 

 where except at the pericardial portion, where the cells still have 

 a columnar shape. The mesenchy matous cells accumulated on 

 the median ventral line of the body are arranged in a certam 

 order to be transformed into the cardiac tube. The third, fourth, 

 and fifth tubules are also markedly prolonged and project into 

 the body-cavity so as to cause the parietal layer of the perito- 

 neum to fold between the epiblast and the body of the tubule 

 (see this Journal : vol. x, Pt. xviii, figs. 8, \\ and 10). Tn some 

 of the embryos, the tubules of the second pair undergo degenera- 

 tion. I have met with, in this series of sections, the same con- 

 dition of the sixth tubule as on the riglit of fig. 86, tlie right 

 tubule having entirely disajipeared. 



Period 4. 



The embryos in the next advanced stage (Stage v) are much 

 diminished in size, assuming a form of a retort or of a pistol 

 ('97, fig. 1, F). Figs. 98-106 represent sections through an 

 embryo of this stage. The posterior larger section of the fore- 

 gut comprising the pronej^hric region, has been reduced into a 

 slender tube [fg.) which is bounded by almost a single layer of 

 high cylindrical cells. The parietal layer of the peritoneum as 



