PLATE 1 



EXPLANATION Or FIGURES 



The figures on this plate are drawn from an injection of a 6-mm. larva of 

 B. palustris. The blood vessels are shown in a primary system comparable to 

 that of other vertebrate embryos. This is the first injection in which the lymph 

 heart appears, attached to the third intersegmental vein. Use a hand lens to 

 secure depth relations. 



90 



