160 Huxley, Bird-watching and Biological Science. lApril 



can seize hold of it — is given entirely by its value to the pair and 

 to the offspring. 



On the other hand, many of the details of the ruff itself, and of 

 the mode of shaking, are non-utilitarian. To carry out its function 

 successfully, any courtship-action must stimulate the senses in a 

 way which must be either pleasurable or startling, or a combina- 

 tion of both, and to this condition the erected ruff of the Grebe 

 conforms — it affords a brilliant combination of black, chestnut 

 and white, which, in addition, is only revealed when the ruff is 

 erected. The general principles of the action are thus determined; 

 but the origin of many of the details we can only look upon as 

 accidental. As far as the position and color of the ornament is 

 concerned we can only say that the Grebe family " shows a tend- 

 ency" to develop crests and ruffs on the head, and that any bril- 

 liant pigmentation they possess runs to black, warm browns, 

 yellows, and whites, while that of other birds runs to other colors 

 — in the Woodpeckers to scarlet, in the Parrots largely to greens 

 and yellows, and so forth. These things are " accidents," in the 

 sense that they are determined by unknown peculiarities in the 

 constitution of the species. 



The form of the action itself, however, is largely a matter of 

 correlation. Many water-birds can be seen to shake their heads 

 from side to side at intervals, especially after preening themselves, 

 and from observations on the curious connection between this 

 courtship-action and actual preening in the Grebe, I have no doubt 

 that it is a specialization of the casual head-shaking after preening.' 



Finally there is a modification of the typical action of shaking 

 which is seen under the influence of jealousy, and is characterized 

 by exaggeration of all the normal behavior (Huxley, '14, p. 511). 

 This is a matter of psychological correlation — takjB a Sensori- 

 motor arc connected with mental processes; increase the intensity 

 of the mental processes, and you increase the intensity of the 

 actions which are the end, i. c. result of that activity. 



To get an example of an action which is determined through 

 inheritance alone, we must go to another species. The Ringed 



• Huxlpy, '14, p. 515. In a similar way the elaborate courtship ceremonies, as seen in the 

 Grebe and many other species, in which twigs are used and held in the bill, doubtless take 

 their origin in nest-building. 



