174 ECOLOGY AND LIFE HISTORY OF THE COMMON FROG 



releasing those that are not fat enough to be females with eggs, and 

 which croak. They considered that the females are released after 

 spawning merely because they become thinner. In R. pipiens. Noble 

 and Aronson consider that the cessation of the female's warning croak 

 is due to the pressure of the eggs, but in R. temporaria this is not so, as 

 can be seen from my description of the female that croaked although 

 she had not laid her eggs, but had probably retained them too long. 

 Moreover, the dismissal sign-stimulus, which, according to my 

 observations, is remarkably effective, was not interpreted in the same 

 way. For example, Aronson pointed out that observations on a number 

 of American species of Rana had shown that the warning croak of the 

 female does not return for several hours after spawning. Noble and 

 Aronson suggested that the dismissal stimulus was probably the 

 resultant of a number of factors, including (i) the ejaculations of the 

 male, (2) the reduction of the girth of the female, (3) the cessation of 

 the female oviposition reflexes, (4) the movement of the female from 

 the egg-laying posture. 



Now these observations are, in my opinion, among the best of the 

 modern work, but I think that the authors have transferred rather too 

 easily observations on their own species to others. Among the 

 European Ranas for example, only R. temporaria and R. terrestris have 

 the horny granules, so that, even in Europe, only these species could 

 show sex-recognition by this means. It is impossible to reconcile the 

 intense grabbing of females by males of R. temporaria with Noble 

 and Farris's description of events in R. sylvatica. 



I think we should recognize that the pattern of behaviour differs 

 much in different species, and that probably neither the American 

 workers nor I were mistaken in what we saw. Much the same can be 

 said about the dismissal stimulus. Aronson found that in Hyla andersonii 

 there was the back-arching sign that I thought was part of the dismissal 

 stimulus in B. hufo. He thought that this alone was the dismissal 

 stimulus. I had suggested that it was really the lack of emission of the 

 eggs after this back-arching that was the true stimulus. Aronson 

 thought that this could not be so in his species, because the back-arching 

 sometimes occurred for a whole day without the male releasing. I 

 have also seen similar imsuccessful attempts to dismiss the male in 

 B. hufo. It is characteristic of instinctive behaviour that it sometimes 

 fails (Tinbergen, 195 1, p. 27), and I merely thought that I was witnes- 

 sing an attempt at dismissal that failed, without considering that it 



