THE STRUCTURE AND AFFINITIES OF HERDMANIA CLAVIFORMIS. 261 



PLATE XIX. 



Fig. 11. A section of the same series from which Figures 9 and 10 (PI. XVIII) were drawn, but from a more 

 anterior position. The right epicardiac tube, e'er, dx., is seen on the ventral side of the pericardium, and 

 the left one, e'er, s., on the dorsal side. 



Fig. 12. A section of the left epicardiac tube showing the thick epithelial wall on one side, and the process of 

 secretion going on on the other side. 



Fig. 13. A section of the part of the two epicardiac tubes at their contact-edges, to show that the epithelial walls 

 are distinct from each other, and that the bridge between the two tubes is mesenchymatous. 



Fig. 14. An oblique section of the ganglion and gland. A few branches, rm dt., of the duct within the gland are 

 shown, as are also the large vesicular gland-cells. 



Figs. 15 and 16. Two transverse sections of the rapheal region from the same series as that from which Figure 14 

 was drawn. In both, the lumen of the rapheal duct is undoubted. It, however, is not recognizabie in 

 some sections of the same series. The ventral process from the duct is shown in Figure 16. 



Figs. 17 to 17g. A series of stages in the development of yolk-granules in the free mesenchyme cells. Figure 17g 

 shows the nucleus in a late granular stage of the cell, after it has become hypertrophied and homogeneous, 

 and of irregular outline. From this on it takes less and less stain, until finally it disappears entirely. 



Fig. 18. An ovary as seen in a total preparation. The beginning of the oviduct and a contained ovum with as 

 yet but a slight development of the test-cells is shown. 



Fig. 19. Section from near the posterior end of an ovary showing the undivided condition of the germinal epithe- 

 lium in this region. The ovum, ov., projecting from the germinal epithelium is nearly ready to escape. 

 Its connection with the stem of the T of the ovary appears in sections farther forward. 



Fig. 20. Section from the middle portion of the same ovary showing the prominent evagination of the epithe- 

 lium in this part; ov.' is a remnant of an ovum evagination from which the ovum has escaped, a 

 "corpus luteum" in other words. 



