340 



RANDOLPH. 



EXPLANATION OF PLATE IL 



LUMBRICULUS VARIEGATUS GrUBE. 



Fig. 6. From a transverse section through a developing tail a little more advanced 

 than in Fig. 5, showing the two lateral mesodermic elements and the composite or 

 double median element. The lateral elements have reached dorsally about half of 

 their ultimate height, and contain neoblasts and smaller embryonic cells. The 

 beginnings of the neural and lateral foundations in the ectoderm appear. The paired 

 foundation of the dorsal vessel is visible, x 520. 



Fig. 7. Showing a transverse section of a slightly more advanced stage than that 

 figured in 6. Ventral blood spaces are present. X 520. 



Fig. 8. From a transverse section of the same series, the fifteenth section anterior 

 to the one in Fig. 7, each section being j^tf '^™- ^^ thickness. Irregular spaces 

 appear in the mesoderm which has reached its extreme dorso-lateral limit {pc). The 

 foundations in the ectoderm are very clearly marked : two ventral foundations, one 

 on each side of the median ventral line, which later unite to form the ventral nerve 

 cord; on each side of these are four foundations of which the upper on each side 

 forms the dorsal setigerous glands, and those next ventral to it the lateral nerve line; 

 the two on each side between the lateral line and the ventral neural foundations 

 correspond to the setigerous and nephric foundations of Lumbricus. x 520. 



Fig. 9. From the same series four sections anterior to Fig. 8, showing the coelomic 

 spaces in the new mesodermic tissue : one in each of the lateral elements and one in 

 each median element. The last-mentioned spaces later unite to form the coelomic 

 space between the ventral nerve cord and the ventral blood vessel. X 520. 



All the figures drawn with the camera. 



