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separated from the rest of the mesoblast, and running in the length 

 of the embryo. This is joined, at each segment, to the walls of the 

 body cavity, by equally solid columns of cells, the primative segmental 

 tutules. I can see no evidence that the tubules form first and then 

 join the Wolffian duct as has frequently been described. At x fig. 2 

 are some cells joining the somite with the rest of the tissue: they 

 are differentiating to form connective tissue. 



In a chick of 40 hrs., fig. 3 A, where the somite has differentiated 

 into two layers, the cells which had formed a swelling (W.D.) in the 

 last embryo have now arranged themselves around a central cavity, 

 apparently formed by vacuolation between them. In alternating sections 

 fig. 3 B this Wolffian duct can be seen to join the cells of the body ca- 

 vity by tubules S.T. The solid rod in fig. 2B have vacuolated so that 

 the body cavity extends right up to the Wolffian duct. 



Pig. 3. 



Fig. 3. Chick of 40 hrs. (A) The cells of Wolffian duct have arranged them- 

 selves in a circle round a central aperture. The duct is not separated entirely from the 

 neighbouring cells. (B) The segmental tubule has begun to vacuolate from the body ca- 

 vity right up to the Wolffian duct. 



Fig. 4. Chick of 47 hrs. (A) A well marked muscle plate has now formed from 

 the outer layer of mesoblastic somite. Its epithelial like cells are continuous with those 

 lining the body cavity. (B) In alternating sections the cells of the muscle plate turn 

 inwards at o while the cells of the Wolffian duct and segmental tubules are continuous 

 with the cells lining the body cavity. 



In a chick of 47 hours, fig. 4 A, the Wolffian duct has more fully formed, 

 and has sunk into the tissue surrounding it. The outer cells of the 



