“Although sponges have many different types of cells, most are not organized into organs with discrete functions, like kidneys, livers, or ovaries (although the choanocyte chambers could be considered simple organs). For this reason, sponges are sometimes described as having a ‘tissue-level’ organization. Some sponges have astonishing powers of regeneration, so extreme that they were the inspiration for regenerating aliens in the science-fiction television series Doctor Who. The defining experiments that revealed this property were published in 1907 by Henry Van Peters Wilson of the University of North Carolina, USA. Wilson mashed up a living sponge and passed it through a fine cloth, the sort used for sieving flour, thereby splitting most of it into individual cells. Wilson then observed that these cells gradually crawled back together and reassembled into a new sponge! Furthermore, if the cells of two different species were mixed together, they would sort themselves out and regenerate into the two original sponges again. Although regeneration is found in many branches of the Animal Kingdom, no other animals are as expert as some of the sponges.”