230 EDWIN G. CONKLIN. 



The rows of muscle cells show clearly along the left side ; the dorsalmost row of the 

 right side also shows and between these two is a clear line, the nerve tube (or cord); 

 anteriorly this cord leads to the wedge-shaped light area at the anterior border of the 

 larva, which is the sense vesicle (brain) and which is still open to the exterior. The 

 test cells somewhat obscure the posterior portion of the tail. 



PHOTO 24. Tadpole a little older than the preceding viewed from the right side. 

 The tail is much elongated and the muscle cells, each faintly marked by a clear nu- 

 cleus and dark outline, are also elongated as compared with preceding photos. Two 

 rows of muscle cells are distinctly visible, the third also comes into view at the hinder 

 end of the tail. There are seven or eight cells in each row as indicated by the num- 

 ber of nuclei. The gastral endoderm shows as a dark area in the trunk. The neural 

 cord and tube is the clear area on the dorsal side of the trunk, its anterior limit being 

 marked by a flattened contour line where the neural folds are just closing. 



