March 25, 1986

The withdrawal this month of two major players from videotex - the business of offering information and services through computers in the home - does not signal the end of the industry, but may well help redirect it, most analysts believe. Knight-Ridder's termination of its Viewtron videotex service last week because of a lack of consumer interest, came just weeks after the Times-Mirror Company said that it would end its Gateway videotex service in southern California, also because of a lack of response from consumers. These moves followed the Centel Corporation's sharp cutback of its Keyfax service in the Chicago area last year for the same reason. What all of these efforts had in common, experts say, is that they tried to offer too much to too many people who were not overly interested. Instead of leaping to use computerized banking and shopping services and to call up news, advertising and other information on a video screen, most users found little cause to change the traditional ways they had always done those things.

Prime Minister Yasuhiro Nakasone and other Japanese officials have begun trying to talk down the value of the yen, which last week hit its highest level against the dollar since World War II. The comments, along with lower oil prices, lifted the dollar sharply yesterday. It ended the trading day in New York at 179.32 yen, up from Friday's 176.05. In early trading in Tokyo today the dollar rose still further, to 180.60 yen, but traders attributed that rise to the military clash between Libya and the United States. Political tensions often lure traders to the dollar.

THE subject of sexual reproduction, an exasperated Charles Darwin concluded more than a century ago, ''is as yet hidden in darkness.'' It still is. But the origins of sex have become the subject of a spirited debate among biologists who are pondering theories that range from the prosaic to the bizarre. None of these new theories is flattering to males of any species. At best, males are portrayed as useful sources of genetic variety. One theory justifies males as storehouses of redundant information that females can draw on, if necessary, to repair damaged genes. Another describes sex as a sort of disease, with males mere agents of contagion.

CHICHEN ITZA, Mexico - Eleven hundred years ago the massive pyramid of Kukulkan was built by the Mesoamericans in a clever feat of ancient engineering so that the shadow of a snake moves along the balustrade of a stairway as the sun sets during the vernal and autumnal equinoxes. To the viewer grounded in objective reality, the shadow that looks to be a snake slithers along the stairs and vanishes with the setting sun. But in the viewer's imagination, it clearly slithers away from the stairs straight ahead to the nearby sacred cenote, or pool, where the ancient people made sacrificial offerings of precious possessions and, sometimes, people. But archeologists cannot agree on the meaning of the shadow. Indeed, the shadow and the argument over it symbolize the increasing importance being attached to the astronomical practices of the Mesoamericans. Astronomical studies in the last decade have led to a new and highly sophisticated understanding of the ancient observations of the sky. Using these discoveries and other scientific findings, archeologists and researchers of other disciplines are reinterpreting the history and culture of the ancient Indian races that inhabited Mexico and Central America.

Small homemade bombs were fired this afternoon at the United States Embassy and the Imperial Palace, the police said. There were no injuries, and no damage was reported. The bombs appeared to have been launched from parked cars outside the United States Embassy and the western gate of the Imperial Palace, known as the Hanzomon Gate, according to the Tokyo Metropolitan Police.