by Knopf, $8.95. Uncle Oswald reminisces about his attempt, in the early 1920s, to tap all the geniuses of the period for a sperm bank. His weapons were a scientist who had been tinkering with the artificial insemination of cows, a beauty named Yasmin who was willing to tinker with anybody, and a remarkable aphrodisiac pill. This looks like a recipe for pornography, and to some extent the novel is exactly that, but mere pornography is repetitious. Mr. Dahl’s scheme permits him to have disrespectful fun with Proust and Shaw and such great names. Repetition is minimal. An uneven book and hardly for the delicate, but it has its high points..