18 T. H. BURLEND, 



Gut begins 1,28 ; foregut ends 2,24 ; neurenteric canal 5,33 — 5,39 ; 

 heart extends from 1,43—2,23. 



In tliis embryo, which shows signs of abnormal development, 

 the first traces of the kidney on the left side are visible in 2,40. 

 For a few sections 3.5, 3,6 and 3,7 the structure is of the nature 

 of a groove in the somatic layer of the lateral plate mesoderm 

 immediately beloAv and lateral to the nephrotorne. 



Although from 3,8 onwards the outgrowth is solid it is not very 

 prominent until about the middle of segment VIII after which it 

 is very pronounced and becomes twisted also. 



As we pass posteriorly the insertion of the outgrowth into the 

 mesoderm gets further and further from the coelom. This is due 

 to a gradual receding of the coelom from the protovertebra the 

 further caudalwards we pass. 



The duct begins at 4,1 but from 4,3 to 4,9, and again at 4,12 

 and 4,13 it is extremely difficult to distinguish the duct from the 

 underlying mesoderm. 



This series suggests very strongly that the duct is formed by 

 difi'erentiation from the mesoderm. At 4,14, 4,13, 4,12, 4,6 and 4,4 

 it looks as though mesoderm proliferation is occurring for this 

 purpose. 



The duct ends at 4,14, but there are indications of an uneven 

 outline of the somatic mesoderm and also signs that cells are pro- 

 liferating from this region to form the duct as far back as 4,27. 



Hence the segments affected on the left side are: post, half 

 of VI, VII, VIII, IX, X with a duct beginning in the post, region 

 of X and ending at the post end of segment XI'?. 



On the right side the kidney begins as a groove from 3,5 to 

 3,10 and continues backwards as a more or less solid outgrowth 

 until 3,45 or 3,41. The duct becomes distinct at 3,45 and ends at 

 4,28, viz. in segment XII. 



There is suggestive evidence of the recent splitting oft' of the 

 mesoderm which forms the duct from the mesoderm of the lateral 

 plate. 



Thus the segments affected on this side are VI, VII, VIII, 

 IX and ant. portion of X, whereas the duct extends over the post, 

 region of X, and also over XI and XII. • 



