The multiplicity of potential teratogenic mechanisms requires that a rapid and practical screening system for adverse effects on development must be able to assess not just one or two developmental events but as much of the entire phenomena as possible because it is not yet possible to explain the mechanism on triggering event for any teratogenic outcome.
Artificial hydra "embryo´ is obviously quite different from a real embryo on first inspection. On closer examination, however, it seems to share a great many developmental capabilities with any ontogenic system.
Sequence of events the "embryo" undergoes during reaggregation and regeneration, such as spatial orientation, cell sorting, recognition of neighbors and formation of cell junction, formationa of extracellular material, tissue organization, response to induction and formation of organ fields all appear to be similar to those events required during mammalian embryogenesis.
In addition, the "embryo´ 1) has an obvious and complex ontogeny, 2) reacts to a teratogen in a dose-related manner, v) has an evident threshold effect to the drug, 4) illustrate that developmental critical periods exist and that the developmental stage at the time of insult is more important per-baps than the severity or nature of the insult, 5) reacts in a somewhat stereotyped manner and 6) the system itself, also can provide the two relevant dose levels based on toxicity as adequately as standard laboratory rodents but at a significantly lower cost in time and effort.
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