SOME "COLD-BLOODED'' LOVERS 173 



Phryniaxus nigricans, at the breeding season, utters a 

 call note which consists of two clear, musical " rings," 

 followed by a long descending " trill " like that of our 

 British Greenfinch. But, it is to be noted, both sexes 

 in this case perform. 



The period of sexual activity with perhaps the majority 

 of animals is intermittent and extends over but a short 

 period annually ; with others potency is continuous, 

 at least with the males, though desire becomes clamant 

 only when aroused by external stimuli. But whenever 

 this condition be aroused it invariably finds expression 

 in exaggerated movements or vocal demonstrativeness. 

 It uses the normal channels of expression, in short, but 

 intensifies them. Now this period of sexual activity 

 represents the maximum of " fitness " in animals, and 

 it is not surprising, therefore, to find that when the 

 barometer of vitality stands high some approach to the 

 maximum of activity is indicated. In many birds this 

 is revealed in song, though the earlier stimulating cause 

 is absent. Among the cold-blooded frogs the same 

 obtains. In the Edible Frog (Rana esculenta), for example, 

 the males, which " are great musicians," remarks Dr. 

 Gadow, " go on singing for sheer enjoyment not only 

 during the pairing time, but throughout the months of 

 June and July. Warm, moonlight nights are the favourite 

 times for the concert, which takes place in the water, 

 beginning at sunset and continuing till early dawn. A 

 few individuals utter a single note, * gwarr-oo-arr ' or 

 * coarx,' but these are only preliminaries. The pre- 

 centor . . . begins with a sharp-sounding * brekeke,' 

 and this is the signal for all the others to chime in with 

 the same note, varied with all sorts of other sounds, bass, 

 tenor and alto, each performer filling its resounding vocal 



