742 Comparative Animal Physiology 



year, except immediately after an egg-laying period, by injection of mac- 

 erated anterior lobe of the pituitary.^^^' ^^^' ^^^' ^^^' Preparations of pituitaries 

 from females are about twice as effective as those from males. The ovula- 

 tion, which will occur between the second and fourth days, includes rup- 

 ture of the follicles and expulsion of the eggs by contraction of smooth mus- 

 cle fibers in the follicle wall. Injection of pituitary extract into male frogs in- 

 duces amplexus.. These sex reactions in amphibians may also be induced by 

 pituitary extracts from other amphibians, from fishes, ^'^^ mammals,^^'* or 

 may even occur in response to antuitrin-S from pregnancy urine. 



Premature spawning has been induced in several species of fishes after 

 injection of fresh pituitary glands from other fishes. The ovoviviparous fish 

 Cnasterodon was caused to spawn more than two weeks before the normal 

 time after treatment with pituitaries from Micropagon and Luciofimelodus.^'- 

 The Brazilian species, Pimelodus"^^ and Prochilodus,^^^ which normally 

 spawn after the heavy rains that in Brazil follow a long period of drought, 

 were induced to produce eggs and sperm during the period of drought 

 within 1 to 3 days after an intramuscular injection of pituitaries from these 

 same species. Rainbow and brown trout, Salmo gairdnerii and S. fario, in 

 Wisconsin, were caused to produce mature eggs and sperm 6 to 7 weeks 

 before the normal spawning season by intraperitoneal injections of fresh or 

 acetone-dried pituitary glands from the carp.'^^ FSH from sheep and serum 

 from pregnant mares were without such effect. Increase in size of the ovo- 

 cytes and ovaries of the lamprey, Petromyzon, and precocious sexual ma- 

 turity were observed after treatment with human pregnancy urine. *'^' ^^ 

 Hypophysectomy in the killifish, Fundulus, is followed by regressive changes 

 in the ovaries and testes, compared with controls. ^^^ When the gland is re- 

 moved in the autumn the gonads fail to undergo their normal spring en- 

 largement. Furthermore, implantation of adult pituitaries at 3 day inter- 

 vals into immature Fundulus induces within 4 weeks a considerable degree 

 of gonadal activation in both sexes, together with production of secondary 

 sexual pigmentary changes in the males characteristic of the breeding sea- 

 son."2 



Gonadal Hormones. Hormones arising in the gonads regulate the male and 

 female characters of the body. They stimulate the development and activ- 

 ity of the accessory reproductive organs, and control the sexual behavior of 

 the animal. Although the influences of these hormones are basically similar 

 among all vertebrates there is considerable difference among species, and 

 even among individuals, as to their detailed actions. 



There are three types of gonadal hormones, androgens, estrogens, and 

 progestins, all three types being elaborated by both sexes. The chief sources 

 of these hormones, as the name gonadal hormones implies, are the ovaries 

 and testes, although other organs such as the placenta and adrenals may 

 also contribute significant quantities. All the naturally occurring gonadal 

 hormones possess a steroid nucleus, but recent studies of active synthetic 

 substances appear to indicate that their activities do not depend on this struc- 

 ture. 



The androgens mainly regulate the development and activities of those ac- 

 cessory reproductive structures functionally important in the male. The es- 

 trogens are mainly concerned with the development and activity of those 



