78 THE CONDOR. Vol. XXI 
young capon in whose body the ovaries of a hen are grafted, will develop the 
feathering characteristic of the hen. The capon without the engrafted ovaries, 
will develop almost as the normal male. A normal female rabbit, treated by 
hypodermic injection with the extract of foetus in normal salt solution, will 
pluck the fur from her breast and build a nest as though expecting a litter of 
her own young, though none are developing. In these two cases a structurai 
and a psychologic character, respectively, are influenced by a physiologic agent 
—a particular chemical substance. This substance is secreted and thrown into 
the blood stream by the germ cell or by the developing ovum, and constitutes 
one of those products, so important to the highly organized animal, which we 
term internal secretions. 
The germ cells in birds, like those in most other wild animals, are season- 
ally active. As a result the reproductive gland may increase or di- 
ininish in size from ten to one hundred fold in regular cycles, which cycles are 
generally conformable to season. With the fluctuation in mass there will be a 
change in the amount and possibly in the nature of the internal secretion, hence 
the whole physiologic balance of the body will be seasonally affected. It is 
doubtless because of this ebb and flood of the physiologic tide that certain in- 
stincts, particularly those connected with the reproductive process, appear and 
disappear in orderly sequence each year. 
It is maintained that the choosing of a mate is a purely instinctive act on 
the part of the wild bird. (It might often be discovered to be so among our 
august selves!) The choice is part of a great chain of events connected with 
the reproductive process as a whole; it is physiologic in its immediate origin, 
and therefore is of seasonal recurrence. During the dormant period of its re- 
productive cells, the bird is practically an asexual creature. Maleness and fe- 
maleness have disappeared entirely so far as interests, many activities, and 
often external appearance, are concerned. On the other hand, resumption of 
the germ cell activity initiates a new mating activity. The bird chooses a new 
inate. 
So much for the theorist. What have we from the field observer? Among 
the forces that hold individuals together in the bird world, we may recognize 
at least three bonds, the parental tie, the. marital tie, and the social tie. Of 
these three, which is of most importance as a bond of some duration? I ¢on- 
tend that the parental tie is of greatest survival value to the race. We find it 
lacking in but few species, notably in cowbirds, in Old-World cuckoos, and in 
megapodes. But in these species the marital tie is also lacking as a persistent 
bond. The flocking tie alone, persisting in the cowbirds, results in a reprehensi- 
ble Bohemian freedom and a Gypsy-like vagrancy of most unavian character. 
Upon the duration of the parental tie, the whole care of the young and 
hence the safety of the race is hinged. It must outlast the period of the young’s 
dependency, while the marital tie is not absolutely necessary beyond the mo- 
mentary contact required for impregnation. We actually see the parental tie 
ruptured. The parent weans her young because of waning instinct, and fur- 
ther support is denied it. The parent and her offspring then become rivals, 
peaceful or otherwise. If such a fundamental tie be ruptured, why not also 
the less necessary marital bond? We find at least circumstantial evidence bear- 
ing upon the question. 
At the close of the breeding season, a thousand Linnets assemble in a weed 
patch, there to feed from time to time during the fall and winter. The flock 
