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71.
This paper surveys in broad perspective some of the steps inthe development of theones of mammalian sex differentiationfrom antiquity to the present. The questions of why and howmales and females differentnte and why there are intersexeshave been answered by conjectures, speculations, and theones.In antiquity, when the existence of mimimhan egg and sperm wasunknownsex determination was con]ec tuicd to depend upon such factorsas which testis contiibuted the semen or which sideof the uterusreceived it. These fanciful notions peisisted until the middleof the 18th centuiy. Discovery of mammalian sperm in the samecentury and the ovum in the 10th centuiy led to obseivationsof fertilization. With advances in genetics andthe identificationot sex chromosomes, the 20th century was prepared to constructtheories foi normal sev differentiation and inteisexuality basedon experimental observation. The bovine freemartina naturalexperimentprompted the hounonal theory leseaich on frogsled to a coittco medullaiy inductor theory, cellular cmmerismin fteemaitin and co tvun was the basis for a cellular theory.Of these, the hormonal theory in particular, provided some verifiablespeculations. However, there is no completely acceptable theoryand new lines of research are badly needed 相似文献
72.
73.
Radiochromatographic studies of 131I-treated Aurelia polypsrevealed synthesis of three compounds tentatively identifiedas monoiodotyrosine (MIT), diiodotyrosine (DIT), and thyroxine(T4). One compound, MIT, is found within 8 hr after 131I administration,before the detection of DIT or T4 which appear within 24 hr.T4 is not usually detected after 48 hr although MIT and DITwere found up to the segmentation period. None of the compoundswere detected in ephyrae treated with 131I for 24 hr. Administration of low dosages of the goitrogens, thiourea,,propylthiouracil, and potassium thiocyanate, in conjunctionwith iodide, prevented strobilation induction. Radiochromatographyof jellyfish given the goitrogens and 131I revealed a reduceduptake of iodide and an impairment of the synthesis of the iodinatedcompounds. Jellyfish use thyroxine directly for strobilatioa inductionas demonstrated by 131I - labeled T4 administration. The T4was detected in the polyps up to the 48-hr period of strobilationduring which time some of the T4 was excreted into the medium,as was some 131I. The fact that T4, synthesis has thus far been found only instrobilating forms of Aurelia suggests that T4 is involved primarilywith the differentiation of new structures which occurs duringstrobilation. 相似文献
74.
75.
The mimicry, population ecology1 , adult behaviour and life cycle of Heliconius xanthocles were studied at two sites in Colombian tropical forest. The results were compared with the known biology of other Heliconius species. H. xanthocles is probably unpalatable and is a Mullerian comimic of some other species. In the Amazon basin H. xanthocles belongs to the 'dennis ray' mimicry ring of the Heliconiini, which includes Eueides tales, H. bumeyi, H. elevatus, H. melpomene and H. erato. In the Rio Negro valley, where the latter species either do not exist or have different mimetic allegiances, the 'clennis-ray' pattern of H. xanthocles breaks down. The adults are pollen-feeders, like other Heliconius. but they also visit other food sources such as bird droppings. During a mark-recapture programme in the Rio Negro, adults were found to be almost entirely restricted to small areas near their foodplant Passiflorapraeacuta. Females were rarer than males, but this was probably due to a behavioural difference between the sexes. The males had a Fisher-Ford survival rate of 0.95 per day and a life expectancy of 19 days. Population size estimates of males were between 11 and 17 individuals. These estimates are lower than, but comparable to those for other Heliconius. Males as well as females visit the larval toodplant, and an adult male was observed hovering over a small group of larvae. The females lav batches of 12–41 eggs. The largest batch (41 eggs) was laid cooperatively by two females. The larvae are gregarious feeders on shoot-tips of Passiflora praeacuta. and all lile stages are described for the first time. Predation on the larvae by a bug is described. The pupa has a distinctive morphology unlike that of other Heliconius. The adult population ecology, mimicry and larval behaviour are discussed. 相似文献