Wrack beds are accumulations of seaweeds of various kinds that have become detached from the rocks on which they have grown and have been cast up on to the sea-shore. If such accumulations are formed beyond the high tide level, they may remain but little disturbed for several days or even for months. Here, as they gradually decompose, these wrack beds become the home and breeding place for many invertebrate animals* It is with these animals that this thesis is concerned. The most prominent of them are various species of flies, beetles and amphipods, and with them there occurs, less obviously, various mites, oligochaetes and nematodes. over and above these regularly occurring animals there are numerous incidental visitors to the wrack beds.