THE BREEDING BEHAVIOUR OF THE FROG I7I 



each of the species I have studied, there is a special sigii-stimuhis that 

 ensures synchronization. In Bomhitia variegata, the female, just before 

 she begins her swift spinning movement round the weed on which she 

 lays her few eggs, reaches back with her foot and rubs the male on the 

 region of his symphysis pubis. He immediately responds by expelling 

 sperm, and the pair spin round the weed rather faster than the eye can 

 follow, the eggs being laid during this astonishing manoeuvre. In the 

 Common Toad, Biifo hufo, the female stretches herself, and this acts as 

 a sign-stimulus for the male to place his feet at the cloaca of the female. 

 A part of the egg string is then extruded, and glides over the feet of the 

 male, who then pumps sperm over the eggs. In R. temporaria, there 

 is no definite action of this kind, and I think that the sperm emission 

 stimulus is provided by the stream of eggs striking the male over the 

 symphysis pubis, as in Bombina. No similar stimulus ever reaches the 

 male during his life in the pond, for although he crawls over and 

 among eggs already laid by other frogs, these are shppery, and quite 

 unlike the sticky newly-laid spawn. 



Dismissal Stimulus 



In the 1934 paper, I used the term "release stimulus" to denote the 

 stimulus given by the female to the male, which induces him to release 

 his hold upon her. "Release mechanisms" and "releasers" have now 

 come to mean something more general in the literature on animal 

 behaviour, namely, any sign-stimulus that "releases" some kind of 

 behaviour in another animal. For example, the gaping reaction of 

 young thrushes is "released" by a moving object over 3 mm in dia- 

 meter above the horizontal plane passing through the nestling's eyes 

 (Tinbergen, 195 1). Curiously enough, my "release stimulus" is also 

 a releaser in tliis new sense, but it is better to avoid using the same word 

 for two things. W. M. S. Russell found the same difficulty and used 

 the term "unclasping stimulus." This has a rather narrower meaning 

 than my term. 



The female R. temporaria that has just deposited her eggs is now a 

 different animal both in appearance and behaviour. She is now at least 

 as thin as a male (Fig. 46), a fact that contributes to her release if she 

 is molested v/hile she is making her way out of the pond. She is, 

 however, still provided with the badge of her sex, the horny granules, 

 and she is liable to be seized by any male that touches her. When this 

 occurs, she no longer feigns death or remains silent, but behaves 



