86 T. H. BURLEND, 



Explanation of the Figures. 



The left side of each of the Plate-figures is the right side of the 

 embryo and vice-versa. 



List of reference numbers : 



Fig. 1, Transverse section of Embryo A about the middle of seg- 

 ment III (section 2,17). The condition of the mesoderm and the primi- 

 tive kidney groove in this region of the body are shown. 



Fig. 2, Trans, sect, of A (section 3,8), This passes through the 

 beginning of protovertebra VI on the left side of the body and slightly 

 further back on the right side. 



Note the early condition of the primitive kidney groove before the 

 somatic and splanchnic layers of the mesoderm are properly diflferentiated. 



Fig. 3. Embryo A (section 3,17). Passes through hind end of 

 protovertebra VI on the animal's left side and behind the segmented region 

 on the right side 



Note the condition of the kidney rudiment on each side. 



Fig. 4. Embryo B (section 3,8). Through beginning of proto- 

 vertebra VI on left, and through hind end of this same protovertebra on the 

 animal's right side. 



The ectoderm above the kidney rudiment is slightly grooved. 



1 



