326 
On the Nest and Egijs of the Common Tern 
much consideration wo are unable to substantially modify the assumed order of 
mottling of the previous paper. In broad lines we have : 
TABLE XII. 
Mottling 
Mean Breadth 
1913 census (391 eggs) 
1914 census (1108 eggs) 
Confluent blotches, d + i/-\-g 
Transition Forms, a + h ... 
Discrete, Copious, c 
Discrete, Sparse, k + f+i 
2-97 
2-97 
2-99 
2-96 
3 03 
2- 95 
3- 02 
3-01 
The value of polyserial tj con-ected for class index correlation of mottling is 
•1753 for the census of 1914. It is therefore certainly within the probable error 
of the difference. Now in both cases the confluent mottling gives a greater 
bi'eadth than the discrete and sparse mottling, but the transition forms a + b, 
and c, are anomalous. The correlation ratio tj in both cases is significant and 
shows a relation, not very intense, between mottling and bi-eadth, but in the 
present stage of the mottling classification it is certainly not possible to unravel 
the relationship. The 1914 returns undoubtedly seem to indicate that not only 
the confluently but the discretely mottled eggs have the greater bi-eadths, the 
lesser breadths being found in the transition forms. It should be noted that the 
returns for 1914 being nearly four times as numerous are worth twice as much. 
If we could really lay any stress on the sign to be given to the association, we 
should have to assert that in the species at large the rule is opposite to that for 
the individual hen. In her case the broader egg has less mottling, while in the 
species the broader egg has the greater or at least the more confluent mottling. 
The former relation overrides any result to be obtained from the species as a 
whole, and seems to oppose any theory that greater pressure during transition 
through the oviduct is the source of greater mottling*. 
We have further worked out the associationf of Index and Length to the 
Mottling. We have 
Mottling and Breadth 
Mottling and Length 
Mottling and Index 
Census 
1913 
•1803 
•1550 
•0850 ± •0203 + 
Since the probable error is of the order 02 we see that the value is insigni- 
ficant for length. On the other hand the order of mottling classes in the three 
* The time of transition through the oviduct may conceivably be a factor of greater importance, 
t Obtained from polyclioric rj with correction for number of arrays and the class index correction 
for mottling. 
J t)q is the mean value of the correlation ratio on the assumption of uo association. 
