76 



and where the lateral plates are almost cut off from it. The epithe- 

 lial like cells of the lateral plate instead of passing into the outer 

 layer of the somite turn round into each other. There is at this stage 

 only questionable evidence of the formation of the Wolffian duct. 



Fig. 1. 



B.C. 



Fig. 1. Chick 32 hrs. (A) Mesoblastic somite M. 8. differentiated into inner and 

 outer part. Towards and right up to the former which is solid the body cavity runs B.C. 

 The epithelial like cells of somite are continuous with those of lateral plates. (B) View 

 of sections alternating with A. The mesoblastic somite has not differentiated into two 

 layers. The epithelial like cells do not run in continuity with those of the lateral plate. 

 At x a few cells are seen at juncture. 



Fig. 2. Chick of 38 hrs. (A) A proliferation of cells on dorsal aspect at juncture 

 of mesoblastic somite and lateral plate is the first indication of Wolffian duct W. D. 

 Otherwise the epithelium of somites continues into lateral plate. (B) Somite here to seen 

 in alternating sections with A. The epithelium of somite is cut off from lateral plate 

 and the Wolffian duct is connected by a solid rod of cells, the segmental tubule with 

 the epithelium of body cavity and proliferated cells at juncture. 



In the chick of 38 hours (fig. 2 A) the broad base — intermediate 

 cell mass — from which the dorsal lateral plate springs from the 

 somite is seen to have become swollen, probably from proliferation 

 of cells at that region. 



This marks the situation in this region of the developing Wolf- 

 fian duct, which consists therefore of a solid growth, not as yet diffe- 

 rentiated from the rest of the mesoblast. In sections alternating with 

 the above, fig. 2B, the epithelial like cells of the lateral plate do not 

 form a series continuous with those of the somite; they run inwards 

 towards the middle line as a solid column ending in what appears 

 like a round knob, S.I., and W.B. This appearance, simular to a 

 round knob, is a section of the primative Wolffian duct, and its 

 cells are continuous with those of the swellings W.D. fig. 2 A). 



The Wolffian duct arises therefore as a solid rod, not as yet 



