194 OUR” BERD VALELIES: 
markings. The rule is by no means an invariable 
one, however, and very often the difference between 
the intruded egg and those among which it is placed 
is so great, that one cannot but wonder how it is that 
the owner of the latter fails to detect the imposture. 
As to the reason for the absence of parental affec- 
tion upon the part of the cuckoo many theories have 
been put forward, only two of which seem to be 
worthy of consideration. 
The first of these is to the effect that the eggs of 
the bird are deposited only at long intervals, so that, 
were a nest to be built in the ordinary manner, the 
duties of maternity would be spread over a very long 
period of time, and the mother would have simul- 
taneously under her care eggs, newly-hatched young, 
and full-fledged offspring. This supposition, how- 
ever, seems purely conjectural, and rests upon no good 
evidence. 
The second and more plausible theory is based 
upon the fact that the sexes of the bird are ill-balanced, 
at least five males being found to every female. It is 
therefore suggested that the unfortunate members of 
the weaker sex are so persecuted by the attentions of 
rival suitors that they really have no time for nest- 
making, and are forced to transfer their family 
duties to others with fewer calls upon them. Be 
this as it may, the fact remains that the cuckoo 
never brings up its own offspring, and affords us one 
of the most curious cases of perverted instinct to be 
found in the whole of the animal world. . 
Much more is there to be said with regard to this 
