4. HORMONES AND BEHAVIOR
211
ity of the evidence for a direct effect is not questioned. Not even in
cyclostomes and elasmobranchs (124) is there any reason for doubting
that the gonads and secondary sexual characters are hormonally controlled. Aronson (57), reviewing the results reported following gonadectomy and the results reported following treatment with testosterone
propionate, methyl testosterone, pregneninolone, estradiol, and a variety
of hormonal and nonhormonal substances, is more reserved. The persistence of male behavior following castration was noted in a number
of fishes and led to the suggestion that testicular secretions are more
important for the ontogeny of this behavior than they are for its maintenance in the adult. A similar possibility for the ovarian hormones does
not seem to have been considered.
The likelihood that the hormones produced by the gonads of fishes
are steroids was long ago deduced from effects of artificial and mammalian steroids on the secondary sex characters of fishes, and from the
effects of extracts of fish gonads on mammalian tissues normally responsive to steroids (125-127). Direct evidence was provided by the extraction of androgenic substances from the testes of silver salmon
(128),
chum salmon (129), and the dogfish Scyliorhinus stettaris (130, 131);
and of estrogens from dogfish ova (132), of estrogenic substances and
possibly progesterone from lungfish ovaries (133), and of estrogens from
the ovaries of Torpedo marmorata (130). The estrogen obtained from
the ova was identified as estradiol-17/?, which is thought to be one of
the principal estrogens secreted by the Graafian follicle in mammals;
estrone is the other (134). The estrogens from the lungfish ovaries were
estriol and estrone, with a trace of estradiol-Πβ, whereas those from
Torpedo ovaries were estriol and estradiol-17/3 in a proportion of 2 to 1.
The important generalization that the ovaries of all vertebrates produce
estrogens seems justified (133).
The site of origin of the gonadal hormones of fishes is discussed in
recent reviews (126, 127, 130, 135, 136). Forbes (135) and Hoar (126,
127, 136) especially stress the uncertainty with respect to the cellular
origin of the male hormone and attribute this uncertainty to the failure
of so many investigators to identify interstitial cells in the testes of
certain fishes. The question seems to have been clarified by Marshall
and Lofts (137, 138). They explain that two distinct endocrine arrangements occur in the testes of fishes. One is the typical interstitial cell pattern of vertebrates and has presented no problem. The other is a complex of perilobular connective tissue elements which undergo a cycle
essentially similar to that of the interstitial cell cycle in seasonal birds.
Functionally, both arrangements are considered similar to the permanent
interstitial or Leydig cell unit present in most mammals. Histochemical
211
ity of the evidence for a direct effect is not questioned. Not even in
cyclostomes and elasmobranchs (124) is there any reason for doubting
that the gonads and secondary sexual characters are hormonally controlled. Aronson (57), reviewing the results reported following gonadectomy and the results reported following treatment with testosterone
propionate, methyl testosterone, pregneninolone, estradiol, and a variety
of hormonal and nonhormonal substances, is more reserved. The persistence of male behavior following castration was noted in a number
of fishes and led to the suggestion that testicular secretions are more
important for the ontogeny of this behavior than they are for its maintenance in the adult. A similar possibility for the ovarian hormones does
not seem to have been considered.
The likelihood that the hormones produced by the gonads of fishes
are steroids was long ago deduced from effects of artificial and mammalian steroids on the secondary sex characters of fishes, and from the
effects of extracts of fish gonads on mammalian tissues normally responsive to steroids (125-127). Direct evidence was provided by the extraction of androgenic substances from the testes of silver salmon
(128),
chum salmon (129), and the dogfish Scyliorhinus stettaris (130, 131);
and of estrogens from dogfish ova (132), of estrogenic substances and
possibly progesterone from lungfish ovaries (133), and of estrogens from
the ovaries of Torpedo marmorata (130). The estrogen obtained from
the ova was identified as estradiol-17/?, which is thought to be one of
the principal estrogens secreted by the Graafian follicle in mammals;
estrone is the other (134). The estrogens from the lungfish ovaries were
estriol and estrone, with a trace of estradiol-Πβ, whereas those from
Torpedo ovaries were estriol and estradiol-17/3 in a proportion of 2 to 1.
The important generalization that the ovaries of all vertebrates produce
estrogens seems justified (133).
The site of origin of the gonadal hormones of fishes is discussed in
recent reviews (126, 127, 130, 135, 136). Forbes (135) and Hoar (126,
127, 136) especially stress the uncertainty with respect to the cellular
origin of the male hormone and attribute this uncertainty to the failure
of so many investigators to identify interstitial cells in the testes of
certain fishes. The question seems to have been clarified by Marshall
and Lofts (137, 138). They explain that two distinct endocrine arrangements occur in the testes of fishes. One is the typical interstitial cell pattern of vertebrates and has presented no problem. The other is a complex of perilobular connective tissue elements which undergo a cycle
essentially similar to that of the interstitial cell cycle in seasonal birds.
Functionally, both arrangements are considered similar to the permanent
interstitial or Leydig cell unit present in most mammals. Histochemical