"To-night you saw the hybrid that the invaders sent to recapture Ruth and me. It was a fit specimen of the grisly magic which those devils from outer space work with their uncanny surgery and growth-stimulating radioactive rays. The basic element of that monster was an ordinary tarantula spider, with its growth incredibly increased in a few short hours of intensive ray treatment in the Centaurian's camp. The half-head grafted to it was that of a human being. They always graft the brain cavity of a mammal to a hybrid--half heads of burros, horses, or even dogs, but preferably those of human beings. I think that they prefer to use as great a brain power as possible. "The hybrids are controlled through the small opalescent globes on their heads, globes that are in direct tune with a huge master globe of opalescent fire in the invaders' camp. When Ruth attacked you after you placed the opal head-piece upon her head, she was for the moment merely another of the invaders' servants blindly obeying the broadcast command to kill. The white globes that Ruth and I wore when we escaped from the camp were identical with those worn by the invaders themselves, being nothing more than harmless insulators against the effect of the green moonlight." A sudden spasm of pain convulsed Crawford's face. Dixon sprang forward to aid him, but the old man rallied with an effort and weakly waved Dixon back. "I'm all right, Bruce," he gasped. "My strength is nearly exhausted, that is all. Like a garrulous old fool I've worn myself out talking about everything but the one important subject. Bruce, have you developed that new and infinitely powerful explosive you were working on?" "Yes," Dixon answered grimly. "I have an explosive right here in the laboratory that can easily blow the Centaurian's camp completely off the map." * * * * * Crawford shook his head impatiently. "Destroying the camp would do no good. We must shatter the space ship itself if we are to extinguish those green rays in time to save our world." "That is impossible if the space ship is hovering up there by the moon!" Dixon protested. "No, it is not impossible," Crawford answered confidently. "I have a projectile in my laboratory that will not only hurtle across that great gap with incredible speed, but will also infallibly strike its target when it gets there. It is a projectile that is as irresistibly drawn by radio waves as steel is by a magnet, and it will speed as straight to the source of those waves as a bit of steel will to the magnet. "The Centaurians in the space ship," Crawford continued, "are in constant communication with their camp through radio apparatus much like our own. If you can pack a powerful contact charge of your explosive in my projectile, I can guarantee that when the projectile is released it will flash out into space and score a direct hit against the walls of the space ship."