Peptides serve as important signalling molecules in development and differentiation in the simple metazoan Hydra. A systematic approach (The Hydra Peptide Project) has revealed that Hydra contains several hundreds of peptide signalling molecules, some of which are neuropeptides and others emanate from epithelial cells. These peptides control biological processes as diverse as muscle contraction...

For his Second Labor, Heracles was tasked with slaying the Hydra, a serpentine monster from ancient Greek mythology who possessed many heads. When attempted to decapitate monster, two new heads grew in place of each severed head, an expression hopelessness such struggle for anyone but hero. The invulnerability Hydra because its one immortal head. Once head cut off, defeated, and Heracles' secon...

Understanding the evolution of development in large part relies on the study of phylogenetically old organisms. Cnidarians, such as Hydra, have become attractive model organisms for these studies. However, despite long-term efforts, stably transgenic animals could not be generated, severely limiting the functional analysis of genes. Here we report the efficient generation of transgenic Hydra li...

Hydra games were introduced by Kirby and Paris, for the formulation of a result which is independent from Peano arithmetic but depends on the transfinite structure of 0. Tree ordinals are a well-known simple way to represent countable ordinals. In this paper we study the relation between these concepts; an ordinal less than 0 is canonically translated into both a hydra and a tree ordinal term, ...

Hydra is a computer hardware description language that integrates several kinds of software tool (simulation, netlist generation and timing analysis) within a single circuit specification. The design language is inherently concurrent, and it offers black box abstraction and general design patterns that simplify the design of circuits with regular structure. Hydra specifications are concise, all...

Chimeric hydra were prepared by recombining epithelial and interstitial cells between 3 strains of hydra of different sizes (maxi, normal, and mini strains). The resulting chimeras generally resembled the epithelial cell parent more than the interstitial cell parent in size, budding rate, tentacle number, and form. This suggests that epithelial cells normally exert considerable influence over h...