120 



BIOLOGICAL LECTURES. 



does not contribute any secondary prototroch cells. In the 

 32-cell stage the material is still in these cells of the highest 

 quartette of the subumbrella. One of them is shown in the side 



ar. 



FIG. 13. Amphitrite trochophore, showing apical tuft, prototroch, paratroch, stomadsema, 

 and one arm of mesoblast consisting of six cells. 



view, Fig. 8, and all three in Fig. 9, shaded with lines. These 

 three cells may be called secondary trochoblasts, although they 

 contain a small amount of material (see unshaded portion of 



FIG. 14. Amphitrite, left side ; prototroch, paratroch ; mouth at arrow ; outline of 

 archenteron stippled ; mesoderm stippled. 



cell in Fig. 8) which does not enter the prototroch. With the 

 next cleavage each of these cells divides so that the six cells, 

 two in each of the three quadrants, contain the material of the 



