366 
The Egg of Ctieulus Canorus 
We note that judged by the coefficient of variation the Cuckoo's egg is more 
variable than the eggs for the sub-groups for 
Length in 12 out of 16 cases, 
Breadth in 10 out of 16 cases. 
It is less variable in both breadth and length in the cases of Robin-Cuckoo and 
Wren-Cuckoo, less variable in length only in Yellow-Ammer-Cuckoo and Reed- 
Warbler-Cuckoo, and less variable in breadth only in Sedge-Warbler-Cuckoo, 
Barred- Warbler-Cuckoo, Whitethroat-Cuckoo, and White-Wagtail-Cuckoo. We 
therefore see that as a rule the egg of the gens is less variable than that of the 
race. 
(2) Oil the Relation of the Gens Egg to the Foster- Mother's Egg. 
Taking these 16 cases and correlating the dimensions of the Cuckoo's egg with 
those of the foster-mother, we find : 
Correlation of length of Cuckoo's and foster-mother's egg* =10, 
Correlation of breadth of Cuckoo's and foster-mother's egg = '24. 
These are not very large values, and the number of cases dealt with is 
only 16, but it does appear that there is some relationship between the size 
TABLE IL 
Bulk-Modulus of Cuckoo's and Foster-Mother's Eggs. 
Species 
Robin 
Garden- Warbler 
Meadow-Pipit 
Wren 
Redstart 
Sedge- Warbler 
Baried-Warbler 
Whitethroat 
irarsli- Warbler 
Red-backed -Shrike 
White-Wagtail 
Pied-Wagtail- 
Reed-Warbler 
Tree-Pipit 
Hedge-Sparrow 
Yellow-Ammer 
Mean 
Standard Deviation 
Size of Foster- 
Size of Frequenting 
Mother's Egg 
Cuckoo's Egg 
4791 
6435 
5197 
5890 
4142 
6145 
2855 
5616 
3724 
6173 
3234 
5944 
5478 
5792 
3831 
5721 
3724 
5872 
6359 
6071 
4877 
6247 
4690 
6071 
2871 
6228 
4560 
6228 
4.322 
6379 
5504 
6044 
4385 mm.^ 
6053-5 mni.s 
959-13 mm.3 
225-72 mm.3 
* Mean Length of Cuckoo's Egg, 22-225 ; of Foster-Parent's Egg, 19-806 ; the mean breadths are 
respectively 16-500 and 14-763 ; the corresponding standard deviations are: Length -3544 and 1-G414 ; 
Breadth -1837 and 1-0971. 
