Charles River Laboratories has signed an agreement to buy the contract research division of the Belgian drugmaker Galapagos for about $179 million. The division includes Argenta and BioFocus, companies that together had sales last year of $87 million. The two companies employ more than 340 scientists, many of whom are chemists, at sites in England and the Netherlands. For Galapagos, the sale will end a strategy of combining internal drug discovery and contract research services. For Charles River, the purchase will add in vitro capabilities to its current in vivo expertise.