Key 4 (MJR, p. 63) is to the Zygomycota (phycomycetes) which are characteristic of dung and amongst the first to appear when freshly dropped dung is incubated. They soon disappear, however, but their fruiting can be prolonged by plating small portions of dung on a nutrient medium (e.g. potato carrot or potato dextrose agar) to which has been added a small amount of antibiotic to reduce bacterial growth. This method is especially suitable for the parasitic and predacious fungi. A cultural approach is essential for the identification of many of these fungi and the above media, and oatmeal agar, are suitable for culture as well as isolation. For this reason the study of this group of fungi is less easy than that of the ascomycetes and basidiomycetes but, because the asexual stages are characteristic, we have attempted to key out the commoner genera which might be found, with notes on common species. The asexual spores are sporangiospores formed in sporangia; some sporangia produce a single spore within a closely fitting sporangium, and have in the past been erroneously described as conidia. A great range of sporangial structure occurs within the orders concerned. The classical structure is the massive (up to 250µm diam.) multispored sporangium with an internal columella which remains after the spores have been dispersed (e.g. _Mucor_); those of _Mortierella_ are similar, but smaller and without a columella. Other sporangia are much reduced and may be only 10-20µm diam., and contain only a small number of spores (_Thamnidium_) or one spore (_Chaetocladium_); these small globose structures are termed sporangioles. Spores may also form in chains; the chains are in terminal groups and are formed by the differentiation of the contents of cylindrical sporangia which are considered to be part-sporangia (merosporangia). When the sporangial wall has disappeared the spore chains may remain discrete and intact, or they may collapse into a wet droplet of spores (_Syncephalastrum_, some _Piptocephalis_). Members of the Kickxellaceae (e.g. _Coemansia_, _Kickxella_) have single spored merosporangia produced in serried ranks on boat-shaped or swollen structures (sporoclades). The sexual spores (zygospores) are rarely seen without culturing; oatmeal agar is one which favours their production. The key includes one member of the Entomophthorales, which also produces single-spored sporangia. Other members of this order may be found parasitising the various animals which live in dung; many other predacious fungi may also be seen, e.g. parasites of amoebae (_Acaulopage_). The key is of necessity far from complete, and omits members of the Dimargaritales, which have been found frequently on dung of small mammals in America.