INTERPEDUNCULAR NUCLEUS 207 



This difficulty is illustrated by the published report of experiments 

 by Aronson and Noble ('45) designed to localize in the brain the 

 mechanisms which mediate specific components of the mating be- 

 havior of male frogs. In hundreds of experiments involving local 

 ablations or transections, there were a few which gave clear-cut evi- 

 dence of precise localization of function. In this connection Dr. Aron- 

 son writes me: "I believe that, while some activities, e.g., warning 

 croak, ejaculatory response, and release of the female by the male at 

 the termination of oviposition, are quite definitely localized, the 

 mechanism controlling other phases of mating behavior are rather 

 diffuse. In the latter cases more precise experiments w^ould, I think, 

 demonstrate diffuseness rather than localization." 



The authors' very conservative analysis of their protocols does 

 reveal a few areas with local specificity of function. Among these is 

 the clasp reflex, which is one of the most characteristic features of 

 this mating behavior. Normally, the mating clasp is relaxed or in- 

 hibited immediately after oviposition, and this presumably involves 

 inhibitory action. There is evidence that the primary center of this 

 reflex is in the spinal cord and that the inhibitory phase is under some 

 measure of cerebral control. Relaxation or inhibition of the clasp is 

 quite consistently abolished by destruction of the preoptic nucleus 

 or dorsal part of the hypothalamus, but this result does not consist- 

 ently follow injury to the habenulae or interpeduncular nucleus. 

 Though the clasp involves the use of skeletal muscles, the reflex as a 

 whole is a visceral reaction related with oviposition and ejaculation 

 of sperm. Cerebral control of the release of the clasp in the hypo- 

 thalamus may be transmitted to the upper levels of the spinal cord 

 by a direct pathway via tr. mamillo-tegmentalis and ventral teg- 

 mental fascicles of group (3), as described on page 278, without in- 

 volvement of the interpeduncular complex. But Dr. Aronson would 

 not limit the inhibitory influence resulting in release to this pathway. 

 Again in personal correspondence he says: "While the spinal clasp 

 center might be quite limited, the mechanism inhibiting or modify- 

 ing the spinal clasp reflex is very diffuse, especially in the midbrain 



and diencephalon The interpeduncular nucleus might well be 



involved here." 



An interesting series of experiments on the Japanese toad reported 

 by Kato ('34) reveals an inhibitory center for the muscles of the con- 

 tralateral limbs in a region described as "on the anterior end of the 

 lamina terminalis," but not accurately defined. The diagrammatic 



