3650 The Zoologist — August, 1873. 



therefore, the tendency which certain habits have to become hereditary in 

 certain animals, we feel compelled to reject the application of this principle 

 in the case of the cuckoo, on the ground that it can only hold good where 

 the habit results in an advantage to the species, and in the present instance 

 we have no proof either that there is an advantage, or, if there is, that the 

 cuckoo is sensible of it. Touching the question of similarity between eggs 

 laid by the same bird, Professor Newton says : — " I am in a position to 

 maintain positively that there is a family likeness between the eggs laid by 

 the same bird" (not a cuckoo) " even at an interval of many years," and he 

 instances cases of certain golden eagles which came under his own observa- 

 tion. But do we not as frequently meet with instances in which eggs laid 

 by the same bird are totally different in appearance ? Take the case of a 

 bird which lays four or five eggs in its own nest before it commences to sit 

 upon them — for example, the sparrowhawk, blackbird, missel thrush, carrion 

 crow, stone curlew, or blackheaded gull. Who has not found nests of any 

 or all of these in which one egg, and sometimes more, differed entirely 

 from the rest? And yet in each instance these were laid, as we may 

 presume, not only by the same hen, but by the same hen under the 

 same conditions, which can be seldom, if ever, the case with a cuckoo. 

 Looking to the many instances in which eggs laid by the same bird, 

 in the same n^st, and under the same circumstances, vary inter se, 

 it is not reasonable to suppose that eggs of the same cuckoo deposited 

 in different nests, under different circumstances, and, presumably, dif- 

 ferent conditions of the ovary, would resemble each other. On the 

 contrary, there is reason to expect they would be dissimilar. Further, 

 we can confirm the statement of Mr. Dawson Rowley, who says, " I have 

 found two types of cuckoo's eggs, laid, as I am nearly sure, by the same 

 bird." (' Ibis,' 1865, p. 183.) It is undeniable that strong impressions upon 

 the sense of sight, affecting the parent during conception or in an early 

 stace of pregnancy, may and do influence the formation of the embryo, and 

 it has consequently been asserted that the sight of the eggs lying in the 

 nest has such an influence on the hen cackoo, that her egg, which is ready 

 to be laid, assumes the colour and markings of those before her. This is 

 not, however, supported by facts. For the egg of a cuckoo is frequently 

 found with eggs which do not in the least resemble it {e. g., those of the 

 hedgesparrow) ; or with eggs which from the nature of the nest could not 

 have been seen by the cuckoo (as in the case of the redstart, wren, or willow 

 wren); or deposited in a nest before a single egg had been laid therein by 

 the rightful owner. Again, two cuckoo's eggs of a different colour have 

 been found in the same nest. If both were laid by one bird, we have a 

 proof that the same cuckoo does not always lay eggs of the same colour ; if 

 laid by different birds, then the cuckoo is not so impressionable as has been 

 supposed. What really takes place, we believe, is this : — The cuckoo lays 



