-2B- 



thoss represented in ^igs. 5 b-1 are enlarged 240 diameters, 

 while those in Figs. 6 a-i are magnified only 90 times. 



A section through the anterior end of the gland, pas- 

 Bing through the point marked a. Fig. 6 k, is represented in 

 Fig. 6 a. The ohief difference, "besides that of size, between 

 this section and the corresponding one of the preceding stage 

 (Fig. 5 f ) , is in the complete development of the cell-groups 

 (gr'.), which in the preceding stage v/ere quite small and unde- 

 veloped. We have now in each side of the gland, which is exact- 

 ly bilaterally sjTimietrical, four gro ups of gland cells, the groups 

 being arranged in pairs, one pair on each side lying near tho 

 middle line, the other being nearer the side (Pigs. 6 e and k, 

 m.c.g. and l.c.g.). This arrangement of the cell-groups into 

 pairs is distinct from end to end of the gland, and for conve- 

 nience they will >e spoken of as the "median" and "lateral" 

 pairs of cell-groups. As h"E been said, the groups gr'. never 

 reach the size of the first developed groups gr. 



The ciliated cells have changed somev/hat since the 

 precedinp stage. They have become relatively, as well as actu- 

 ally, more elongated at certain parts of the ciliated layer, 

 while at other places they are still short and nearly filled 

 with their large oval nuclei. The nuclei of the longer cells 

 are small and circular in outline, and at certain places seem 

 to be more or less regularly arranged near one end or other of 



