PLATE 2 



EXPLANATION OF FIGURES 



9 From an embryo of 5 mm., showing the anlage of the pronephric duct grow- 

 ing from the pronephric anlage at a. The ducts of the two sides are asymmetrical, 

 one side extending over two and the other three somites. The independence of 

 duct and ectoderm is seen at c. The two were in close contact in the living em- 

 bryo but have separated in preparation. The drawing also shows the distance to 

 be traversed by the duct to reach the cloaca. 



10 to 15 Consecutive sections 6 n thick, of a 5 mm. embryo. In figure 10 the 

 duct is attached to the ectoderm by clear protoplasm. Figure 12 shows the cell 

 body and nucleus of the same cell. These sections show that the medium of con- 

 nection of ectoderm and duct is derived entirely from the duct and also the limit- 

 ing membrane between the two layers. 



16 to 24 Consecutive sections, 4 n thick, of a 6 mm. embryo, showing the anlage 

 of the duct from the terminal cell, a, to where it is free from the ectoderm. Note 

 modification of ectoderm at point of contact with duct, the means of attachment 

 of the two and the limiting membrane. The outline of the anlage of the duct is 

 more regular than in last series. 



3G6 



