CELL AflCREaATION AND DIVISION OF LABOR 



89 



The genus Plcodorina furnishes the next two members of the series, 

 namely, Pleodorina illinoisensis and P. californica. The former of these 

 resembles Eudorina elegans in form and appearance. It is ellipsoidal 

 and has 32 cells embedded in a jelly matrix. In the typical condition, 



A ' B C 



Fig. 58. — A, Gonium sociale; B and C, Gonivm pectorale, top and side views. 



however, four cells at the anterior pole of the aggregation are smaller 

 than their fellows. This difference in size does not always exist, for 

 in abundant material every gradation between Eudorina elegans with 

 its cells of uniform size and P. illinoisensis with its four small cells 

 can be found. Pleodorina californica is much larger than P. illinoisensis, 



Fig. 59. — Pandorina viorum, a spheroidal colony. 



and its cells are more numerous. Its cells are always of two sizes, large 

 and small, the proportion of small cells to the total number being much 

 higher than in P. illinoisensis. The structural polarity in the aggregation, 

 due to the difference in size of cells, is very marked. 



