178 



DONALD WALTON DAVIS 



TABLE 1 



Complete 



Complete 



a = 28 



Incomplete 



c = 16 



Incomplete 



b = 16 



d = 9 



The coefficient of association by the formula, 



^ ad — be . 



Q = — , IS - 0.008 



ad + be 



The probable error of Q by the formula, 



1 -Q' 



P. E. = 0.6745 X 



2|/a + b + c + 



d ^ a b c d 



This implies that the demonstrated tendency of j the plane of 

 fission to lie perpendicular to the major transverse axis of the 

 mouth (p. 177) is not so strict as to regard the difference be- 

 tween two adjacent endocoels, the one complete, thej^other 

 incomplete. 



The same facts as were summarized in the left part of table 9 

 have been represented in the corresponding part of table 10, 

 counting separately each bounding mesentery. The bounding 

 mesenteries indicated by symbols in the column headed B in 

 tables 3 to 6 are represented in table 10 in the column headed 

 'Frequency' and in the appropriate rows. Thus each unit in 

 the frequency column of table 10 indicates a position of a division 

 plane on one side of one individual resulting from a division, and 

 the total number of units in the column of frequencies is equal 

 to the number of symbols in all the columns of bounding mesen- 

 teries in tables 3 to 6. In reckoning the total number of 

 divisions in complete and in incomplete endocoels I have sub- 

 tracted the numbers of mesenteries whose apparent complete or 

 incomplete character is in doubt. I have, of course, included 



