Transmission electron micrograph of SP 105 bacter- iophages. Bacteriophages are viruses that infect bacteria. They have no reproductive machinery & rely on the bacterium's to replicate. They attach themselves to the bacterial cell wall using the tail fibres faintly visible here. The ribbed tail contracts to inject the genetic material (DNA) contained in the head into the bacterium. The tail is seen contracted in the bacteriophage at right. The genetic apparatus of the host is commandeered & within 30 minutes virus progeny fill the cell. Magnification: x71,500 at 35mm size, x500,000 at 8x10-inch size. Reference: MICROCOSMOS, figure 5.7, page 92.