378 



HARPER— ORGANIZATION, REPRODUCTION 



have relatively slight diagnostic value for the species. P. asperum 

 like P. Boryanmn may have eight, sixteen, thirty-two or sixty-four 

 cells. Still certain species tend toward higher and others toward 

 lower cell numbers. P. Ehrenbergii commonly occurs with four, 

 eight, or sixteen cells. The rule that the number of cells in any 

 species is a multiple of two, based as it is on the law of cellular 

 bipartition, is very universally maintained and has long been recog- 

 nized. Individuals with fifteen cells instead of sixteen cells or 



Fig. 4. Fig. 5. 



Fig. 4. Pcdiastriim Boryannm. Peripheral cells with two spines very 

 slender for the species. Interior cells with merely a reentering angle to indi- 

 cate the spines. No intercellular spaces. Configuration i -|- 5 + lO- Colony 

 bilaterally symmetrical about the axis m, n. X about 300. 



Fig. S. p. asperum. Cells with two fairly long peripheral spines and two 

 short, blunt basal lobes. Intercellular spaces well developed, the curves which 

 bound them suggesting the origin of the cell lobes by catenoidal deformation. 

 Configuration i + 5 -+- lO- Colony bilaterally symmetrical about the axis 

 m, n. Possible polarites of the cells suggested by the plus and minus signs. 

 X about 600. 



thirty-one instead of thirty-two cells occur, but as Nitardy ('14) 

 has emphasized, they are great rarities and may be properly re- 

 garded as abnormal. The figure of P. intcgntjji given shows only 

 fourteen cells (Fig. i). 



The relative development of the spine is directly correlated with 

 that of the intercellular spaces and we may consider first the organi- 

 zation of a form with well-developed intercellular spaces. Perhaps 



