288 Illinois State Laboratory of Natural History. 



through the two succeeding divisions, which produce the 8- 

 and 16-cell stages. The cupping of this plate, which results 

 in the formation of an ellipsoidal colony, is apparent as early 

 as the 4-cell stage (PI. XXXVII. , Fig. 9) and continues 

 through the later stages (Fig. 11, 13), so that hy the time 

 the 16-cell plate is formed it has almost the curvature of a 

 saucer. With the formation of thirty-two cells the closure 

 of the cup proceeds and is soon completed. The orifice of 

 the cup is directed outward in all cases, and thus the ends 

 of the cells of the daughter colony which are formed from the 

 outer end of the maternal gonidial cell come to lie in the 

 inner side of the cup, and are the inner ends of the cells of 

 the daughter colony. In the matured colonies the young 

 usually lie with their long axes parallel to the surface of the 

 parent. I have not, however, heen ahle to identify the point 

 of closure of this cup with this region or positively with any 

 other. 



The sequence and position of cleavage planes which produce 

 the quadrangular plate of the 16-cell stage is, in the main, 

 similar to that described hy Goroschankin ('75) and Braun 

 (75) for Eudorina and Volvox. Beyond this stage there is 

 some doubt as to the agreement. A full discussion of the 

 subject is beyond the scope of the present paper, for which the 

 following brief description must suffice. The first cleavage 

 plane (I) divides the gonidial cell into two hemispheres along 

 the axis of the cell, and the daughter nuclei, with the sur- 

 rounding protoplasm, are placed close together in the center 

 of the opposing faces of the new cells (PI. XXXVII., Fig. 7). 

 The second plane (II) is at right angles (Fig. 8-9) to the first 

 and also passes through the regions representing the axis 

 of the ancestral cell. In this instance also the nuclei are 

 gathered near the center of the young colony, which exhibits 

 to an appreciable extent the curving indicative of the later 

 formation of the cup. The 8-cell stage results from the 

 divisions of each of the quadrants of the 4-cell stage by a 

 plane (III) which is parallel to one of the previous planes 

 and perpendicular to the other, meeting the latter at a point 

 about midway between the center and the circumference. By 



