parp:xtal behavior 



1317 



liod of estrone treatment. Retrieving, and 

 other aspects of maternal behavior, were 

 shown by these animals after withdrawal 

 of the estrone treatment. Weicliert and Ker- 

 rigan (1942) found that mother rats m- 

 jected with estrogen during the lactation 

 l)eriod allowed the young to become scat- 

 tered over the cage without retrieving them, 

 and that the young were often found cold 

 outside the nest. Similarly Riddle, Hollan- 

 i\cr, Miller, Lahr, Smith and Marvin (1942) 

 found that estrone tends to terminate es- 

 tablished maternal behavior. They report, 

 however, that this does not happen in hypo- 

 physectomized rats. 



Apparently contradictory results have 

 l)een reported by Leblond (1938) who found 

 tliat male domestic mice showed retrieving 

 behavior after estrin treatments or the im- 

 plantation of ovarian grafts. Moore (1919) 

 implanted ovaries in gonadectomized male 

 rats, and reported that they subsequently 

 showed maternal behavior, including re- 

 trieving. Intact male rats similarly im- 

 planted with ovaries did not exhibit such 

 behavior. Similar treatment failed to induce 

 maternal behavior in the guinea pig 

 (Moore, 1921). 



(d) Summary remarks. These data on the 

 hormonal induction of retrieving are rather 

 confused, chaotic, and in many cases con- 

 tradictory. There has not yet been a study 

 of this problem with a design in which the 

 experience gained during the early experi- 

 ments was utilized, or in which the imjior- 

 tance of statistical analysis was antici- 

 pated, or in which a broad range of causal 

 factors was comprehended. 



In spite of these inadequacies, a number 

 of points may tentatively be made. The 

 fact that hypophysectomy and prolactin 

 administration both increase the incidence 

 of retrieving behavior suggests that pro- 

 lactin acts by means of its antigonado- 

 trophic effect. However, prolactin increases 

 retrieving behavior both in hypophysecto- 

 mized and in gonadectomized animals, 

 which renders it unlikely that prolactin 

 affects retrieving through either antigonado- 

 trophic or luteotrophic effects. The alterna- 

 tive possibility is that hypophysectomy and 

 prolactin, although they both cause in- 

 creases in retrieving behavior, do so in dif- 

 ferent ways, or through different kinds of 



effects on the animal. Closer qualitative 

 analysis of the fine details of the behavior 

 of animals treated in the various ways re- 

 ported here will undoubtedly reveal many 

 differences that have been obscured in the 

 relativelv crude treatments undertaken so 

 far. 



Certain similarities between the physio- 

 logic bases of nest-building behavior and of 

 retrieving should be noted. Hypophysec- 

 tomy and thyroidectomy enhance both 

 types of behavior. Progesterone induces 

 both retrieving in rats and nest-building in 

 mice. Even more suggestive, estrogen treat- 

 nrent seems to have the same effect on both 

 types of behavior. It inhibits it during 

 treatment, but causes it to rise above the 

 pretreatment level after withdrawal of the 

 hormone treatment. However, the fact that 

 prolactin induces retrieving behavior (at 

 least in rats), whereas it does not have any 

 effect upon nest-building behavior in the 

 mouse, suggests that the physiologic bases 

 of the two types of behavior are not entirely 

 identical. Coordinated study of both types 

 of behavior in both species would obviously 

 be useful. 



Induction of retrieving behavior by ex- 

 ternal STIMULI. As Beach (1951) pointed 

 out, the stimulation of retrieving behavior 

 by stimuli provided by the young really 

 presents two quite different problems. First, 

 it is possible that stimuli provided by the 

 young can induce a physiologic state which 

 underlies the capacity to display retrieving 

 behavior. Secondly, there is the problem of 

 what stimuli induce an animal that is physi- 

 ologically capable of retrieving to do so, 

 and to retrieve some objects rather than 

 others. We shall discuss these problems sep- 

 arately. 



ia) Induction of readiness to retrieve by 

 stimuli from the young. Wiesner and Sheard 

 (1933), who found that only about 20 per 

 cent of nulliparous, nonpregnant female 

 rats would retrieve young offered to them 

 by the experimenter, succeeded in arousing 

 readiness to retrieve in many of the "non- 

 retrievers" by confining them in cages with 

 young rats for several days, the young be- 

 ing replaced every 2 days by fresh ones. By 

 this procedure, which Wiesner and Sheard 

 called "concaveation," retrieving behavior 

 was induced in 25 out of the 74 nonreactors 



