Bacteria-free hydra, cultured in sterile media, were fed bacteria-free larvae of Artemia salina. Normal growth and budding were obtained in symbiotic and aposymbiotic Hydra viridis. Two nonsymbiotic hydra species did not form buds under bacteria-free conditions. When these hydra were fed nonsterile Artemia, or if the medium was reinoculated with bacteria isolated from budding stock cultures, normal budding was resumed. An exogenous budding factor, which can be provided by nonsterile Artemia larvae, or even by some bacteria, appears to be required by these nonsymbiotic hydra. This factor is endogenous in Hydra viridis.

River Dan is the largest of the headwater rivers of the Jordan. The karstic exsurgence of the Dan has a seasonally stable output, a long stretch of strongly turbulent flow, stable temperature around 15.5 °C and high oxygen saturation. A total of 156 taxa, mainly at the species level, were identified from the river. These species are almost exclusively of Palearctic origin. About half of the species are limited to the northernmost part of Israel. The faunal complex described, does not present any longitudinal zonation for the 5 kilometers of turbulent flow; neither does it present seasonal changes in species composition. River Dan is considered to be a post-Pleistocenic river which has an important function of refugium for a wide area of aquatic waterbodies in the area, including the presently drained Lake Hula. It is suggested that in the Illies scheme of stream classification, River Dan might represent a type of stream belonging to a 'pseudorhithral' along with other stenothermic warm water torrents of the tropical-subtropical climatic belt.

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