PHYSIOLOGY OF ANTERIOR HYPOPHYSIS 



277 



of breeding site, and avian display and 

 courtship performances (A. J. Marshall, 

 1955, and chapter by Lehrman). 



Thus, for most but not all of the seasonal 

 breeding vertebrates, the primary excita- 

 tions to breeding activity originate in one 

 way or another in the external environment. 

 Those structures most exposed to such stim- 

 uli are the skin and the specialized sense 

 organs, particularly those for seeing, hear- 

 ing, and smelling. It will be recalled that 

 the sight of his mate incubating is sufficient 

 to initiate in the male pigeon the secretion 

 of crop milk (Patel, 1936). It is also not 

 infrequent, especially among birds, that the 

 presence of a mate is a prerequisite for 

 ovulation. Here again, interesting observa- 

 tions have been made on the pigeon (Mat- 

 thews, 1939). The female separately caged 

 and denied sight of other birds does not 

 ovulate; but if she is permitted to view, by 

 means of a glass partition in the cage or a 

 mirror, a separately caged male or even a 

 female pigeon, or is allowed to see the mir- 

 ror image of herself, ovulation and oviposi- 

 tion ensue. The stimulus which causes ovu- 

 lation is clearly visual and not tactile, olfac- 

 tory, or auditory. In sheep the presence of 

 the ram is believed to hasten ovarian activ- 

 ity and estrus in ewes (Riches and Watson, 

 1954; Schinckel, 1954), and it is likely that 

 here both sight and odors play a part. 



It is apparent from observation of the be- 

 havior of domestic and laboratory mammals 

 that strong nasogenital relationships exist, 

 but the effeet-of'sexual odors and olfactory 

 stimulation on the sexual functions has 

 received only cursory study. Pseudopreg- 

 nancy has been induced in rats by simply 

 applying a local anesthetic to the nasal 

 mucosa (Shelesnyak and Rosen, 1938) and 

 similar prolongations of luteal function were 

 induced by bilateral excision of the spheno- 

 palatine ganglion, but not by removal of 

 the olfactory bulbs (Rosen, Shelesnyak and 

 Zacharias, 1940). Local irritants applied 

 to the nasal mucosa likewise did not affect 

 the estrous cycle. These authors felt that 

 the nervous factor involved was limited to 

 the nonol factory innervation of the nasal 

 mucosa. Whittcn (1956a) showed that mice 

 rendered anosmic by removal of the olfac- 

 tory bulbs have significantly smaller ovaries 

 and uteri and fewer corpora lutea. No effect 



was observed in anosmic males. In both 

 male and female mice the body weights 

 were reduced. 



In a recent study Whitten (1956b) found 

 that external stimuli associated with the 

 male mouse modify the estrous cycle in the 

 female. The incidence of mating after pair- 

 ing was greatest on the 3rd night and was 

 low on the 1st, 2nd, and 4th nights. The 

 finding suggests that in some females the 

 cycle was delayed, and in others it was 

 advanced, by the presence of the male. In 

 another experiment in which males were 

 caged in a small basket within the females' 

 cage for 2 days before pairing, the incidence 

 of mating on the 1st night was greatly 

 increased. Since presence of the males' 

 excreta had a similar effect on the recep- 

 tivity of the females, odors were thought to 

 be an important factor in mediating this 

 behavioral response. 



The determinate-laying wild birds, i.e., 

 those which stop laying when the number of 

 eggs characteristic of the species has been 

 laid, probably perceive the stimulus for 

 cessation of egg-laying through tactile sen- 

 sations. Tactile stimuli are also known to 

 come into play strongly during coitus. It is 

 well known that in several mammals (rab- 

 bit, cat, mink, ferret, ground squirrel, short- 

 tailed shrew) ovulation is dependent on the 

 coital excitation of receptor areas not all 

 of which are confined to the genitalia. The 

 neural pathways involved are poorly under- 

 stood. 



Knowledge of the effect of sound on re- 

 productive phenomena is exceedingly lim- 

 ited. It would be interesting to ascertain 

 what sequential role, if any, various songs 

 and mating calls play in releasing the mani- 

 festations of procreative processes. It is 

 probably of no significance that Benoit 

 (1955) failed to alter the sexual maturation 

 in young drakes with continuous noise, and 

 only indicative that Vaugien (1951) found 

 a hastening of egg-laying in parakeets 

 placed in small containers within hearing 

 distance of an aviary where others of the 

 species were mating. Control females simi- 

 larly caged beyond hearing range did not 

 lay. Sound, however, was not the only vari- 

 able in these experiments. 



Thus, many extrinsic factors act in some 

 manner to influence the secretion of gonado- 



